Battery Options for GE Elec-Trak garden Tractor

Greetings,

I seek your DIY battery pack wisdom for a project of mine. Not a solar bank, but rather a 1972 GE Elec-Trak E12M. I scored this little guy a few weeks ago and am excited to revitalize it for mowing this summer. While it’s in overall good condition, the batteries are long gone so I need to source replacements. At first, I was going to buy new GC2 batteries, but the cost of LiFePo4 batteries on eBay and Amazon has come down so much I'm tempted to try those for better performance and easier off-season storage.

These tractors originally used six 6-volt GC2 lead-acid golf cart batteries in series for a total of 36 V. The main drive motor is rated for 1.2 HP while the three mower deck motors are about 1/3 to ½ HP each. Current draw specs were never officially published, but based on GE’s claim that these can mow two acres on a charge and GC2s having a 215 Ahr rating, I estimate it will draw about 60-80 A while mowing, spiking above 100 when hitting thick grass or climbing a hill.

After some initial research, I’ve narrowed down my options to these two:

1. Buy three 12V 200 Ah DC House batteries and wire them in series. DC House’s advertising on Amazon and eBay claims they can support 170 A discharge.
2. Buy six 12V 100 Ah DJLBERMPW batteries and wire them in a 2p3s arrangement. I emailed DJLBERMPW and they said this arrangement supports up to 150 A discharge.

I picked these because the GE’s battery boxes limit the size and number I can stuff in, and also because I prefer a “ready-made” solution instead of building my own cell packs. I’m heavily leaning towards Option 1 because of the simplicity of only three batteries.

Based on your experience with high-draw battery banks:

• Do you see any concerns with DC House or DJBEL batteries?
• Are there any reasons to pick a series-parallel arrangement instead of three-in-series if both meet similar current requirements?
• These batteries have internal BMS; do you recommend any other external control components? I will be using a power meter to watch amp-hour usage, and all motors have circuit breakers on them.
• Are there any other suggestions or options you’d recommend?

Most appreciated,
Elec-Trakker

I learned about those recently, they are cool.

I would not put 12v batteries in series they can't stay balanced. I would look for a 36v Lifepo4 or build one myself.

You can put one 36 in the front and one 36 in the back and wire them in parallel and they will be able to internally balance that way.

For batteries with a BMS I would buy or build 36 volt batteries for a 36 volt system. And I would want to be certain of the startup draw of the motors before proceeding.

Perhaps look at LiFePO4 battery packs for golf carts?

Thanks for the input. I too was wondering about keeping series batteries balanced. Part of my challenge is the GE's battery boxes limit my options due to their size. They were optimized for GC2 batteries which very few battery makers seem to replicate (and the few that do are ridiculously expensive). The rear battery box is 20" x 15" and the front is 20" x 11".

I did find these last night which are not a lot more than the individual 12V batteries. They may just fit by trimming the handles off. Reviews in gold cart applications are positive too: Amazon.com OGRPHY 36V Lithium 100 Ahr Battery

Because power usage specs are so few and far between, I think I will measure the current draw using our camper's 12V deep cycle batteries to get a baseline.

Victron makes 12v form factor batteries that use an external BMS to allow true balancing in series, but the cost of such a victron set would probably be double or more than 2 36v generics.

That's an awesome little tractor.

Good luck on the retrofitting.


I've been wanting to find a motor so I can do a custom retrofit on an old go-kart or lawn tractor to fool around with.

If you haven't already, you should check out the Elec-Trak facebook group. There's also the Elec-Trak Owners Club at https://www.elec-trak.com/ and the Elec-Trak mailing list at https://cosmos.phy.tufts.edu/mhonarc/elec-trak/index.html. The facebook group gets the most activity by far.

I've been using an E15 since 2015 and built my own LFP battery pack a few years ago. I built my pack from raw cells and don't have any experience with commercially built batteries so I can't really make any brand recomendations. I would be wary of the alphabet soup amazon/ebay brands and any claims they make. You'll want around 100ah of LFP to replace the capacity of golf cart batteries. The GC2s are nominally 215ah, but that's at the 20 hour rate. You'd get far less useful capacity under real use. Lead acid is more forgiving of hard use though so if you plan to run a snowblower or tiller, it may be worth going higher capacity or spending extra on batteries that support high current.

For amperage, it depends heavily on usage. Rutine mainenance mowing on level ground may only draw around 35-50 amps with the original blades. Deep grass, and hilly terrain could pull up to 100 amps. I don't suggest modern high lift or mulching blades, they have a habbit of tripping the motor breakers. Starting surge on the mower deck is maybe around 150-200 amps. Starting a snowblower can hit 300 amps. The starting surges last for half a second or so. Your load meter scale originally should have been around 50 amp at the green/yellow line, 100 amps at the yellow/red line and 150 amps at the end of the red zone. The meters tend to drift over the decades though, mine measures 150-160 amps at the yellow/red line. I try to stay under 150 amps snowblowing for the sake of the motor, it gets pretty toasty even in the freezing cold. You're probably less concerned with snow in PA though.

If you're not in a hurry, watch batteryhookup.com for 36v batteries. They recently had a batch of 60ah 36v LFPs that several memeber of the facebook group used to convert, with 2 or 3 in parallel. At least one other converted with 37v mustang mach e modules, that was the highest capacity conversion I know of at almost 16kwh, more than 400ah. 18650batterystore.com sells a 36v 100ah battery from Epoch that looks like it would fit perfect in the rear battery box for $1700, sold out right now though. The Epoch is pricey but rated for 120 amp continuous and 200 amp for 60 seconds, it's also got a built in heater for cold weather charging. From tear down videos, Epoch build quality looks pretty nice. Epoch is still a lot less than Dakota Lithium or Battleborn. I've seen BigBattery mentioned here for golf cart conversions. As I said though, I don't have hands on experience with any commercial batties. Several on the facebook group have built their own batteries like I did, usually using older 180-200 ah plastic case CALB cells. I used Eve 304ah cells, which almost completely filled the rear box.

If you end up using 12v batteries you'll need to make sure they're rated for use in series and a multi-bank charger would be best. Minn-Kota makes 3 bank 12v chargers with an LFP program. I used to use a 3 bank Minn Kota with my old golf cart batteries, was a nice unit. You will need new charger specific to LFP, the original built in charger isn't suitable for any lithium chemistry. I've got a generic golf cart LFP charger now, it's not great but gets the job done and the BMS doesn't complain about it.

One more detail about converting is you may want to add ballast weight back to the tractor. My pack is 150 lbs by itself but left the front box empty. I've kept 100lbs of concrete blocks in the front to help with steering.

Thanks for the comments and additional feedback. I have seen some of those golf cart battery replacements from the better names but am trying to keep the battery budget under $2000. This tractor will mainly be a novelty item, but I do intend to use it to mow occasionally and pull trailers around our yard. I may even want to mow with it more once I start using it! No plans to till or snowblow since I don't have the attachments and don't really need them.

@JMe15: Thank you for your experience, that is most helpful. I have been reading a lot on the cosmos threads, but when I tried joining the elec-trak.com forum I never got a reply for my sign-up submission. That website has a copyright date of 2013...is anyone still working it? I can't even see posts on that site due to "permissions"...

Does your E15's custom battery have 100 Ahr capacity? How long can you run it or mow with it? I was aiming for 200 Ah with lithium replacements, but if 100 Ah gives the original GE-specified time of 2-2.4 acres that will more than meet my needs (we mow approximately 1.7 acres) and may convince me to spend the money on a better quality pack. DJLBERMPW and Ogrphy have gotten good reviews too. A friend of mine has been pushing me to build a custom one as well.

Can the motors handle 48v?

@Elec-Trakker My pack is 304ah with Eve 304 ah cells. It was an exercise in cramming absolutely as much capacity in the rear box as possible with LFP. I snowblow a long driveway and large parking area and the old lead acids weren't nearly enough. 1.7 acres should be doable with 100ah, though you may want to go through all the motors and check the brushes and bearings, maybe replace the gear oil in the transaxle. A little extra friction here and there can add up and really reduce run time. As for my run time while mowing? I dunno. I'm only mowing about 1/2 an acre, but it's very uneven, on a hillside, and awkwardly shaped, and the front mount deck takes a lot of space to turn around. All the same, i'll go the whole mowing season only charging a few times. LiTime also has a 100ah 36v golf cart battery for 1200. They claim 200amp continuous and 650amp 1 second surge. No personal experience again, but the LiTime name seems well liked here. I'm sure the cheaper batteries would work fine too as long as they have the surge capacity, at least 200amps for a few seconds to be one the safe side. That mostly depends on the BMS, the 100ah cells are usually rated for 200amp for 30 or 60 seconds. Cheap or expensive, you'll also want to upgrade to a T class fuse, good idea for safety, and these tractors like to collect gremlins.

The elec-trak.com forum actually migrated to a new host in the last couple years, dunno why the old copywrite date. To be fair though, I haven't gone on since it changed hosts.

@Bkord The main drive motor would probably be fine at 48v but the 1970's control system is built for 36v, 48v might burn something up. The deck motors would spin too fast, probably overheat, maybe cook the magnets. I've dreamt about going 48v, if only because 36v pure sign wave split phase inverters seem to be unicorns.

Got it, good to know. I saw those LifTimes too and they are on my short list. I certainly intend to give this thing a good going-over, including the bearings and brushes, once I get it to my house (currently stored at a friend's house). We tested it out a couple weeks ago with three 12-volt batteries and confirmed everything electrical works, including the deck motors. It's in quite good shape overall. Only one wire out of the entire harness has been replaced after all these years. We just needed a couple new golf cart contactors to make it move.

The voltage question did raise a concern of mine: Is 43 V of a fully charged lithium concerning too, or is the risk lower since that's only a few volts above 36V nominal, whereas a fully charged 48V lithium set will be at 51V? I know electric motors can handle a little extra voltage but am not sure how "tough" these old GE motors are.

36 and 48 are just easy numbers to say/type for discussion. Lead acid voltages are complicated but a fully charged and rested 18s flooded lead acid (6 golf cart batteries) could measure from 37.8 to 39.6. The onboard charger may output up to 45v. A 12s LFP is nominally 38.2, charged and rested 40.8, charging voltage between 42-43.8. A 16s LFP is nominally 51.2 and charged at 54.4. So a "36v" 12s LFP is comfortably in the ballpark of a "36v" lead acid and perfect for the tractor. All the motors have their individual thermal breakers, so as long as you stick with 36v nominal, overheating shouldn't be a problem unless theres a mechanical problem with the motor.

Sounds good. That's what I figured but wanted to confirm since I know the motors for these tractors are not easy to find if they go kaput.

This looks OK, but doesn't fit:

$1,890 36V RAPTOR 2 – 3.84kWh LiFePO4 | 150a_cont (300a_5 sec) | 21.1W_15.3D_7.4"H_79.3# | 10yr warranty |

What about three LiTime 12v_100ah_tm (trolling motor) batteries in series? Will Prowse video on LiTime_tm web below:
$300 L13_W6.77_H8.43" (group 31 size) _23.4# | 100a_const | 300a_5 sec | 500a_1 sec |

& possibly paralleling a 12s2p 8ah_headway bat to help with surge

Or maybe?

$1,200 L20.47_W10.59_H8.66" (group 8D size) _63.1# | 200a_const | 650a_1 sec |
_still ~1/2" too long: 20.47" vs 20" GE Electrak battery box | Trim ends? |

Robert Mate said:

What about three LiTime 12v_100ah_tm (trolling motor) batteries in series?

Click to expand...

The problem with 12v batteries in series is they can't stay balanced. They will need an active balancer or manual balancing.

I say don't overthink it. Go ahead and buy three off the shelf 12v lifepo4 batteries and run them in series. (Just make sure the bms they use allows for more current then your worst inrush currents)

Then buy three cheap voltmeters, hook one up to each battery and mount them on the dash somewhere. If the batteries get out of balance it'll catch your eye the day it starts to happen and you can top off the low one or bleed out the high one when you get around to it.