Ryobi Zero-Turn Mower SLA to LiFePo4 Conversion - (Updated - Build Complete With Pics!)

[Balsman225]

I've finished my build and successfully mowed my yard with the new battery. 100 Ah cells, 16s Overkill BMS. Mowed my entire yard 0.8 acre on 22° slope using 30% of the battery capacity (80% → 50% SOC). One nice thing: with the old SLA OEM setup the fuel gauge would swing 20-30% depending on whether the battery was under load ( voltage vs SOC lookup table I presume ). I never knew that the actual percent was with the SLAs. With the shunt it's really nice knowing the exact SOC.

Max current while mowing with the new battery 108 Amps as reported by Overkill app, which did make me a little nervous. It must've been very brief since the 100A OEM battery fuse didn't blow. My old OEM battery was the 70Ah SLA. It might be placebo effect, but the mower seems peppier going up hills (shedding almost 200 pounds of lead and having more max current to work with I presume). I noticed no difference in center of gravity change: the mower doesn't seem any more likely to tip.

• The design I used is a modded version of @rio 's brilliant build, here are the changes I made
  • added the middle lid notch to accept the steel lid brace (rough cut using a jigsaw)
  • used high quality 1/2" birch plywood for the sides and bottom, 3/4" for the lid and middle spacers
  • box held together with #6 screws and waterproof wood glue
  • middle spacers screwed into side
  • outside finished with 3 coats of spar polyurethane
  • 5 mm EVA foam (white Cosplay foam from Hobby Lobby) to pad the hold-down braces under the lid
  • 3d printed shunt holder, dust cap and stabilizers for middle brace, and the mains dust cap
  • used this enormous stepper bit to enlarge the hole for the shunt display, took 10 minutes with hand drill
• I destroyed my OEM charging port by plugging in the AIMS Charger the first time causing a large arc from (we suspect) the inrush current filling the charger capacitors from the battery. I have a complaint filed with AIMS Corp to see if this is normal. Here's how I repaired:
  • removed OEM charger receptacle and plug
  • replaced with Anderson SB50 plugs
  • 3d modeled the receptacle to hold the SB50 onto the mower (see pics)
  • connected the blue wire from the lockout circuit to battery positive, permanently disabling the lockout†
  • going to build a $20 protection circuit to prevent this moving forward using a diode and resistor in parallel
  • for now I have been disabling the battery using iOS app, then connecting AIMS charger, last turning battery on to charge without arcing

Here's a full Tinkercad of my build. I've been keeping SOC max 80% for battery life. AIMS charger set to charge LiFePo4 @ 15 amps. Planning to add a mechanical timer, estimate how long it will take to reach ~80% and have it turn off after that duration.

† With rio's help we reverse engineered the lockout circuit in case anyone wants to see how it works, and how I decided to connect the lockout circuit to battery positive, see pic.

New comer here, I have read through the this thread a few times and I want to start out by saying thanks you for for all the great info and sharing your experiences. I am starting to gather up the parts to convert my RM480e. It sat in the garage all last year since the SLA are totally dead and I'm ready to get it running again with a new setup.


Do you happen to have an STL for the Andserson SB50 plug you made for the charger? I purchased the AIMS charger that was mentioned several times I figured I might as well swap out the original charger plug while I’m doing the build so I don’t have any arcing issue like you did the first time.

 

[tommywatson]

Ryobi Riders seems to have an off the shelf solution...

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https://www.facebook.com/groups/ryobiriders/permalink/811469620073205/

 

[Kavalliero]

Hopefully now that it is spring and the folks in colder climates are now starting to get their mowers out of the shed for use...and watching this thread a bit more closely to provide feedback.

As an update to my conversion project:

I still haven't figured out the whole jumpstart issue and why it looks like the four AmpereTime 12v 100ah lithium batteries seem to just kill the power to the mower if I try to turn on the mower when it hasn't been receiving a direct charge for more than 30 min even though the batteries are are between 80-100% charge. I suspect there is something with the BMS in one or more of the batteries but I haven't been able to prove it. So my default procedure was to turn on the charger to get some juice flowing..then turn on the mower with the charger on, then turn off the charger and remove the plug. Wonky experience but seemed to do the trick for my first 4 mows without issue.

After my first couple successful mows only using about 30-35ah of charge of the 100ah available I decided it was working with the hassle of this initial "jumpstart" and just recycled my old SLA batteries. However on my 4th mow everything worked fine until my last pass when the power just suddenly dropped out and shut off the mower. I rolled it back to the shed...plugged it into the charger..the battery monitor lit back up and showed I had only used about 27ah charge and was at over 70% charage. I was able to turn it on and drive it around, but within a few min of turning on the blades the power would fully repeat and cut out again. My amp readout never showed me going over 70amp and it would even cut out sitting still and just running the blades consuming only 20-25amp. So it was't a voltage issue, charge issue, or amperage issue.

I hit the same problem again on my 5th mow where the power would just drop out after using about 27ah of charge. So at least it is a little consisent on where the power fails but I don't know why. Even though these four 12v100ah ampereTime batteries are rated for series installs and the runtime use and discharge is well within their limits it just seems like something the bms doesn't like. It seems like under the worst loads the amps will peak around 75amps and under normal conditions I'm between 45-55amp or less. I don't know how much more time and money it is worth to invest further in this from my perspective unless someone has some good advice on how to troubleshoot this issue vs cutting my losses and buying a new mower and trying to sell this one as used that is designed with lithium in mind. It could be the mower, something with the charger, or something with the AmpereTime batteries.

Living in Florida I never stop mowing...I just mowed less between nov-feb. We are in full on spring now with temps back in the mid 80s. So I don't have time to mess around during my next 9 months of heaving growing. If I don't find an answer to salvage this project I'm either back to my backup push mower or investing in something new.

Help is appreciated.

 

[Supervstech]

Hopefully now that it is spring and the folks in colder climates are now starting to get their mowers out of the shed for use...and watching this thread a bit more closely to provide feedback.

As an update to my conversion project:

I still haven't figured out the whole jumpstart issue and why it looks like the four AmpereTime 12v 100ah lithium batteries seem to just kill the power to the mower if I try to turn on the mower when it hasn't been receiving a direct charge for more than 30 min even though the batteries are are between 80-100% charge. I suspect there is something with the BMS in one or more of the batteries but I haven't been able to prove it. So my default procedure was to turn on the charger to get some juice flowing..then turn on the mower with the charger on, then turn off the charger and remove the plug. Wonky experience but seemed to do the trick for my first 4 mows without issue.

After my first couple successful mows only using about 30-35ah of charge of the 100ah available I decided it was working with the hassle of this initial "jumpstart" and just recycled my old SLA batteries. However on my 4th mow everything worked fine until my last pass when the power just suddenly dropped out and shut off the mower. I rolled it back to the shed...plugged it into the charger..the battery monitor lit back up and showed I had only used about 27ah charge and was at over 70% charage. I was able to turn it on and drive it around, but within a few min of turning on the blades the power would fully repeat and cut out again. My amp readout never showed me going over 70amp and it would even cut out sitting still and just running the blades consuming only 20-25amp. So it was't a voltage issue, charge issue, or amperage issue.

I hit the same problem again on my 5th mow where the power would just drop out after using about 27ah of charge. So at least it is a little consisent on where the power fails but I don't know why. Even though these four 12v100ah ampereTime batteries are rated for series installs and the runtime use and discharge is well within their limits it just seems like something the bms doesn't like. It seems like under the worst loads the amps will peak around 75amps and under normal conditions I'm between 45-55amp or less. I don't know how much more time and money it is worth to invest further in this from my perspective unless someone has some good advice on how to troubleshoot this issue vs cutting my losses and buying a new mower and trying to sell this one as used that is designed with lithium in mind. It could be the mower, something with the charger, or something with the AmpereTime batteries.

Living in Florida I never stop mowing...I just mowed less between nov-feb. We are in full on spring now with temps back in the mid 80s. So I don't have time to mess around during my next 9 months of heaving growing. If I don't find an answer to salvage this project I'm either back to my backup push mower or investing in something new.

Help is appreciated.

I would install 4 volt meters one on each battery and look to see exactly what is dropping out when the mower stops.
You could have a defective BMS or cell in one of the batteries.

Let’s see some pics of how you have them connected to each other.

 

[Supervstech]

Hopefully now that it is spring and the folks in colder climates are now starting to get their mowers out of the shed for use...and watching this thread a bit more closely to provide feedback.

As an update to my conversion project:

I still haven't figured out the whole jumpstart issue and why it looks like the four AmpereTime 12v 100ah lithium batteries seem to just kill the power to the mower if I try to turn on the mower when it hasn't been receiving a direct charge for more than 30 min even though the batteries are are between 80-100% charge. I suspect there is something with the BMS in one or more of the batteries but I haven't been able to prove it. So my default procedure was to turn on the charger to get some juice flowing..then turn on the mower with the charger on, then turn off the charger and remove the plug. Wonky experience but seemed to do the trick for my first 4 mows without issue.

After my first couple successful mows only using about 30-35ah of charge of the 100ah available I decided it was working with the hassle of this initial "jumpstart" and just recycled my old SLA batteries. However on my 4th mow everything worked fine until my last pass when the power just suddenly dropped out and shut off the mower. I rolled it back to the shed...plugged it into the charger..the battery monitor lit back up and showed I had only used about 27ah charge and was at over 70% charage. I was able to turn it on and drive it around, but within a few min of turning on the blades the power would fully repeat and cut out again. My amp readout never showed me going over 70amp and it would even cut out sitting still and just running the blades consuming only 20-25amp. So it was't a voltage issue, charge issue, or amperage issue.

I hit the same problem again on my 5th mow where the power would just drop out after using about 27ah of charge. So at least it is a little consisent on where the power fails but I don't know why. Even though these four 12v100ah ampereTime batteries are rated for series installs and the runtime use and discharge is well within their limits it just seems like something the bms doesn't like. It seems like under the worst loads the amps will peak around 75amps and under normal conditions I'm between 45-55amp or less. I don't know how much more time and money it is worth to invest further in this from my perspective unless someone has some good advice on how to troubleshoot this issue vs cutting my losses and buying a new mower and trying to sell this one as used that is designed with lithium in mind. It could be the mower, something with the charger, or something with the AmpereTime batteries.

Living in Florida I never stop mowing...I just mowed less between nov-feb. We are in full on spring now with temps back in the mid 80s. So I don't have time to mess around during my next 9 months of heaving growing. If I don't find an answer to salvage this project I'm either back to my backup push mower or investing in something new.

Help is appreciated.

If you give up and decide to sell it all, let me know… I might be up for a trip down there.

 

[Kavalliero]

If you give up and decide to sell it all, let me know… I might be up for a trip down there.

See attached photos of how it is all connected. Reused nearly all the existing wiring except adding an extra length of cable between the shunt and the lead negative terminal. I had seen some people directly bolt the shunt directly to the negative terminal using a longer M8 bolt but I didn't feel as confident with that due to the platic shunt bracket preventing direct contact with the battery terminal unless someone says it isn't an issue.

I had removed the plastic battery terminal covers since the Ampere Time batteries seemed to be just a fraction taller than the original Leoch SLA batteries. This prevented the top hold-down bracket from being secured to the frame with the long hex bolt unless I removed the spring washer. I didn't want to use threadlock on the bolt so I just removed the covers so I could keep tension on the hold-down bracket bolt.

The rest of it seemed pretty straightforward except for the "jumpstart" issue and now the sudden power failure.

@Supervstech are you suggesting there is a way to hook a voltmeter up to each battery to test for a specific battery fault while the unit is in operation? If so, please explain. I haven't actually tested this before, but it would seem that the suggestion Option 1 is to get four voltmeters, attach each to the pos-neg terminals of each battery. Drive the mower around and when the power dies, see which voltmeter goes dead. Option 2 would be tp drive around until the mower dies...pull the batteries out of the mower, disconnect the wiring, and test each battery separately.

Of course if all the batteries still read the correct voltage after the power cuts out...that would indicate there is something wrong with the mower control board. Am I following correctly? If so, that seems like some reasonable troubleshooting and sound advice without investing more. If it is a faulty battery then AmpereTime should replace it. The question then would be if the battery failed because of manufacturer defect or if there was something the mower did to cause the battery to fail.

Please correct if I am misunderstanding something.

I have included some pictures of the installed packs. I also have a picture where I show the orginal meter and the new Camway monitor. You can see that the mower only had 87.3 hours on it before I did the conversion and about 3 hours post conversion. So it wasn't even that heavily used before my SLAs gave up the ghost.

If for some reason I decide to give up on this, I would certainly be willing to sell the mower with the batteries. Heck, I may be willing to do that anyways if an offer is reasonable. Feel free to direct message me if that is of interest. Not sure where you're based, but I'm out of Maitland, Florida (suburb on the north side of Orlando).

 

[Supervstech]

Yes, I would get 4 12V digital volt meters, connect one to each battery, and see if one cuts out when the mower fails to run.
100Ah batteries should have no issue with that mower load.

 

[Kavalliero]

Yes, I would get 4 12V digital volt meters, connect one to each battery, and see if one cuts out when the mower fails to run.
100Ah batteries should have no issue with that mower load.

Agreed that the 100Ah batteries shouldn't be having an issue. Well yesterday I mowed again and it only did 20% of my yard. So each time it is mowing less. When I started the mower the AiLi/Camway monitor said the state of charge was at 100% which made sense with the amount of time I let my Dakota Lithium 48v 15ah charger run after each mow. Normally only using about 30-40ah out of the 100Ah batteries. So about 2-3 hours charge is usually sufficient. Dakota doesn't recommend leaving the batteries sit on the charger, so I just installed a mechanical timer to shut the power off after the charge. The Camway monitor seemed to be accurate when reading the voltage, current use, etc...especially for the time I was mowing, so seeing the monitor report 100% charge all seemed to add up.

Well after the mower died I decided to pull the battery packs and test the voltage as well as to prepare for installing the four 12v digital voltmeters. The results were interesting. three of the four packs were all down to fluctuating around 12.89 volts with the fourth (the one supporting the initial Bpos connection for the charger/pack) reading 11.47v. So that puts that battery to about 1-2% charge and the other 3 down to about 15-20% charge. Highly suspect that the batteries would be that out of sync when they were all balanced intially.

It does answer one key question, the Ampere Time BMS didn't actually shutoff the battery since they are were all reading voltages. However, the voltage levels clearly were not where they were supposed to be. However, I'm not exactly sure what this tells me beyond the BMS not killing the battery power resulting in shutting the mower off. With the batteries so low and one so far out of balance I would expect that to cause the mower to behave eratically and power down due to overall insufficent voltage, and clearly there isn't enough charge to actually mow my lawn based on the multimeter results. What I haven't been able to determine is why the batteries are not taking a charge when the Camway monitor said they were.

With the Camway effectively always on since it is wired directly to the batteries through the shunt there is always a trickle current, but for a 100ah battery back and its operational current for the display is less than 50mA this should have been negligible to the charge between mows. There is nothing else wired any differently that I am aware of that would explain a power drain to that magnitude over 6-7 days.

I'm not sure if it is that one low battery has something going on with it that impacted the other 3 and is throwing the charging and everything else out of whack.

I'm currently trying to individually charge and top and balance each battery. I should have the voltmeters in a couple of days. I'll get it all hooked back up in series and see what comes back.

Note that I'm charging through the original charge port. With all the connectors hooked up the same as the original SLA batteries were installed. I wasn't seeing that as an issue unless for some reason the charge wasn't actually flowing as I expected, something with leaving the tri-plug charge handle connected to the charge port even though the charger was off somehow created a slow drain, or one of those other lockout/relay circuits creating some kind of voltage drain over 7 days. Still doesn't explain why the Camway would read 100% though since it is connected directly the battery terminals.

Any insight would be recommended. Seems odd to have these issues where I did the least amount of changes possible to the mower to support the conversion.

 

[HRTKD]

Batteries wired in series can and do go out of sync. A good battery may charge up faster than a lesser battery and once the good battery stops charging (the BMS stops the charge), the lesser battery can no longer get a charge.

If you want a 48 volt battery, build a 48 volt battery. Putting 12 volt batteries in series can lead to problems like you're seeing. That may not be the root cause of your issue, but it could be.

 

[Kavalliero]

Batteries wired in series can and do go out of sync. A good battery may charge up faster than a lesser battery and once the good battery stops charging (the BMS stops the charge), the lesser battery can no longer get a charge.

If you want a 48 volt battery, build a 48 volt battery. Putting 12 volt batteries in series can lead to problems like you're seeing. That may not be the root cause of your issue, but it could be.

Appreciate the input. If the one battery is this far out of whack it could certainly explain part of what I'm seeing. Maybe a replacement battery would be in order, but I am really hesitant to invest even more into the system. A 48v 100ah AmpereTime/LiTime battery would run about $1600 and other brands go up from there. Not really feeling like building a pack with what I have already sunk into this conversion. This is turning into a more costly investment than just replacing with SLA batteries for something as silly as "luck of the draw" on an individual battery. At $1600 I'm 25% of the way towards a more up to date lithium mower from Ryobi, Ego, or Greenworks.

Do you think changing the order of the batteries in the series would help mitigate some of this?

Regardless...frustrating.

 

[fromport]

Appreciate the input. If the one battery is this far out of whack it could certainly explain part of what I'm seeing. Maybe a replacement battery would be in order, but I am really hesitant to invest even more into the system. A 48v 100ah AmpereTime/LiTime battery would run about $1600 and other brands go up from there. Not really feeling like building a pack with what I have already sunk into this conversion. This is turning into a more costly investment than just replacing with SLA batteries for something as silly as "luck of the draw" on an individual battery. At $1600 I'm 25% of the way towards a more up to date lithium mower from Ryobi, Ego, or Greenworks.

Do you think changing the order of the batteries in the series would help mitigate some of this?

Regardless...frustrating.

What about adding a balancer like this one ?

https://www.amazon.com/Battery-Equalizer-48V-Voltage-Balancer/dp/B07L8WKKC3/

 

[HRTKD]

Do you think changing the order of the batteries in the series would help mitigate some of this?

Probably not. The balancer that was suggested in the post above should work, but if you have a bad battery, it's just masking the problem.

 

[Hedges]

Do try fully charging the four 12V batteries independently.
After running until dead as a test, try to determine if one is under capacity for warranty or other replacement. Or tolerable for your application.

Order of series connection won't make any difference.

After full charge as 48V, you can on occasion charge each 12V separately to balance.
Who knows what an equalizer may actually do, might bleed off when you don't want; KISS and just top them off separately.

 

[42OhmsPA]

See attached photos of how it is all connected. Reused nearly all the existing wiring except adding an extra length of cable between the shunt and the lead negative terminal. I had seen some people directly bolt the shunt directly to the negative terminal using a longer M8 bolt but I didn't feel as confident with that due to the platic shunt bracket preventing direct contact with the battery terminal unless someone says it isn't an issue.

I had removed the plastic battery terminal covers since the Ampere Time batteries seemed to be just a fraction taller than the original Leoch SLA batteries. This prevented the top hold-down bracket from being secured to the frame with the long hex bolt unless I removed the spring washer. I didn't want to use threadlock on the bolt so I just removed the covers so I could keep tension on the hold-down bracket bolt.

The rest of it seemed pretty straightforward except for the "jumpstart" issue and now the sudden power failure.

@Supervstech are you suggesting there is a way to hook a voltmeter up to each battery to test for a specific battery fault while the unit is in operation? If so, please explain. I haven't actually tested this before, but it would seem that the suggestion Option 1 is to get four voltmeters, attach each to the pos-neg terminals of each battery. Drive the mower around and when the power dies, see which voltmeter goes dead. Option 2 would be tp drive around until the mower dies...pull the batteries out of the mower, disconnect the wiring, and test each battery separately.

Of course if all the batteries still read the correct voltage after the power cuts out...that would indicate there is something wrong with the mower control board. Am I following correctly? If so, that seems like some reasonable troubleshooting and sound advice without investing more. If it is a faulty battery then AmpereTime should replace it. The question then would be if the battery failed because of manufacturer defect or if there was something the mower did to cause the battery to fail.

Please correct if I am misunderstanding something.

I have included some pictures of the installed packs. I also have a picture where I show the orginal meter and the new Camway monitor. You can see that the mower only had 87.3 hours on it before I did the conversion and about 3 hours post conversion. So it wasn't even that heavily used before my SLAs gave up the ghost.

If for some reason I decide to give up on this, I would certainly be willing to sell the mower with the batteries. Heck, I may be willing to do that anyways if an offer is reasonable. Feel free to direct message me if that is of interest. Not sure where you're based, but I'm out of Maitland, Florida (suburb on the north side of Orlando).

Are you sure they are wired optimally for equal current sharing among the batteries? Positive on the closest battery and negative on the furthest battery.

 

[Kavalliero]

Are you sure they are wired optimally for equal current sharing among the batteries? Positive on the closest battery and negative on the furthest battery.

Yes. The wiring on this uses the series wiring that is the same as the original Ryobi SLA battery install which is setup as you mentioned.

@Hedges do you have a recommeneded load tester for LifePo4 that is good but cost effective? Again, trying to get good results but not trying to dump money into tools, meters, etc...since I'm not into this for the science project aspect of this. lol

I see that Will Prowse had a recommendation to use this Load Tester on his channel.

If the batteries do get out of sync, would there be an issue with adding an Anderson SB50 plug to M8 ring adapter wiring to each battery while all the batteries themselves are wired in series (similar to having a voltmeter connected to each battery)? Disconnecting everything and pulling it out just to be able to access the terminals is a pain in the !@#$@#$.

 

[Hedges]

I have no experience with the load testers.
I tested a battery bank by using inverter to feed electric radiator. Mechanical plug-in timer measured hours.
I tested PV panels with electric radiators in parallel (thermostat on high and knife switch, so the AC switches don't try to switch DC.) DMM measured volts/amps.

Does your mower or charger have a way to report watt hours or amp hours? That would tell you the capacity to first battery shutting down.

 

[Kavalliero]

I have no experience with the load testers.
I tested a battery bank by using inverter to feed electric radiator. Mechanical plug-in timer measured hours.
I tested PV panels with electric radiators in parallel (thermostat on high and knife switch, so the AC switches don't try to switch DC.) DMM measured volts/amps.

Does your mower or charger have a way to report watt hours or amp hours? That would tell you the capacity to first battery shutting down.

The AiLi monitor will report amp hours based on what it sees used, but you need to calibrate it first. I calibrated based on the AmpereTime state of charge table used for their 12v 100ah batteries, but that may not be the most accurate.

 

[Hedges]

Calibrate for amp-hours? or just for SoC?
If it can measure amp-hours then you can know how many Ah the battery or charger provided.

SoC should be reasonably accurate well above knee of curve. But there will be a big change between voltage when charged to 98% vs. rest voltage a few hours later, so need to consider how the monitor deals with that.

 

[Kavalliero]

Calibrate for amp-hours? or just for SoC?
If it can measure amp-hours then you can know how many Ah the battery or charger provided.

SoC should be reasonably accurate well above knee of curve. But there will be a big change between voltage when charged to 98% vs. rest voltage a few hours later, so need to consider how the monitor deals with that.

You can set upper and lower limits on the voltage and an initial Ah for max charge. I took my upper voltage limit from the batteries at rest and applied a lower cutoff limit just above the recommended battery low voltage charge so that it didn't drop below the BMS low limit. From there the monitor can calculate the percentage of state of charge but also shows realtime voltage input/output as well as current in/out and overall Ah it has used. Normally I just leave it showing the Ah amount so I can see how much it consumed, which is why I know it is using only about 30Ah per mow. When I charge it back up it will be back up to the +90Ah limit. When I drive I will sometimes switch to seeing active current just to know the draw...and see it generally around 40A...but when I hit hills or thicker grass while moving it may spike to as high as 81A. Never seen the mower go higher than 85A for a moment where you know it is working hard. Typically it is moving between 40-60A when in motion and 21A on low blade spin and 27A on high blade spin.

 

[Kavalliero]

Update - I charged each battery up separately and reached full charge voltage. I then got a simple battery load tester and currently testing draining each battery separately to validate their charge capacity. So far the "weak" battery in the series string that had much lower voltage than the other three that were basically the same reported tested to have 105Ah capacity for the vs the listed 100Ah. The results showed 1311Wh vs the listed 1280Wh. So based on those results the 12v battery actually had more usuable capacity than listed. Currently testing the other three batteries.

The additional parts for testing are also showing up. I'm not looking to invest the money in a drop-in 48v pack so looking to do the least invasive yet most easily supported model to keeping these four 12v batteries balanced without having to open up the mower and pull the battery tray out to access the terminals. My leading idea is to:
1. Connect the four 12v batteries in series using the original wiring.
2. Install a 12v voltmeter directly to each battery with an included switch in case I wanted to turn off the always-on voltmeter display. This way I can open up the top access cover under the seat and see the state of each battery.
3. Install an Anderson SB50 adapter to each 12v battery so that I can open up the top access cover and top off each battery with a single 12v charger without needing to open up the mower.

Here is the picture install approach I'm looking to do. Any concerns or changes I should be making?