Avoiding sulfation and loss of capacity: How frequently must I charge to 100%?

[Vigilant24]

My planned system is a small, cheap minimalist one for emergency residential loads. Two 12V FLA marine deep cycle (well, kind of) batteries of 105 AH each, so approx 1300 Wh (to 50%DoD) to 2000 WH (80% DoD) of usable capacity. I anticipate years of on-grid float charging with no use, and would like to be able to count on them for 6 months (200 cycles) of heavy use.

Two situations:
1) "Storage": I understand that it's important to keep them at/near 100% capacity during "storage", with occassional desulfation/rebalancing. If I have a good charger that does the "floating" all the time and the "desulfation" on a monthly basis, is adding water all I need to do in addition to that? Should I draw them down 25% or so a few times a year to keep them healthy?

2) Hard use: If I need to use them (50% DoD every day or two), I'm not sure I'll be able to get them back up to 100% with the available solar power that same day. I can probably plan so that the bulk charging is done (to approx 80-90% full) but could run out of sunlight hours before getting to 100%. I'd expect to complete the absorption charge the next day. Will I lose capacity if my batteries frequently remain at 90% charge overnight, or does it take more than 12 hours for the "hard" sulfate to form on the plates? I've read that getting them back t 100% is "critical" (??timeframe??), then elsewhere I see that they shouldn't be left at less than 100% charge for "more than a week." Topping them off every week should be no problem, but getting them there daily is a bigger challenge.

Thanks for any assistance.

 

[OzSolar]

1) Storage:

That's a pretty reasonable approach. I wouldn't be afraid to take them down to 50% or more while you're doing a full system test a few times a year. Also I would keep a close eye on the charger to make sure it's not failed or failing high (it happens) and is boiling off your electrolyte.

Will I lose capacity if my batteries frequently remain at 90% charge overnight, or does it take more than 12 hours for the "hard" sulfate to form on the plates?

Perhaps a very small amount but IMHO in this application your batteries are going to die of old age before cycles or being left slightly discharged gets them.

 

[ArkCabinMan]

My planned system is a small, cheap minimalist one for emergency residential loads. Two 12V FLA marine deep cycle (well, kind of) batteries of 105 AH each, so approx 1300 Wh (to 50%DoD) to 2000 WH (80% DoD) of usable capacity. I anticipate years of on-grid float charging with no use, and would like to be able to count on them for 6 months (200 cycles) of heavy use.

Two situations:
1) "Storage": I understand that it's important to keep them at/near 100% capacity during "storage", with occassional desulfation/rebalancing. If I have a good charger that does the "floating" all the time and the "desulfation" on a monthly basis, is adding water all I need to do in addition to that? Should I draw them down 25% or so a few times a year to keep them healthy?

2) Hard use: If I need to use them (50% DoD every day or two), I'm not sure I'll be able to get them back up to 100% with the available solar power that same day. I can probably plan so that the bulk charging is done (to approx 80-90% full) but could run out of sunlight hours before getting to 100%. I'd expect to complete the absorption charge the next day. Will I lose capacity if my batteries frequently remain at 90% charge overnight, or does it take more than 12 hours for the "hard" sulfate to form on the plates? I've read that getting them back t 100% is "critical" (??timeframe??), then elsewhere I see that they shouldn't be left at less than 100% charge for "more than a week." Topping them off every week should be no problem, but getting them there daily is a bigger challenge.

Thanks for any assistance.

I can't help but think that golf cart batteries, which are true deep-cycle batteries, would hold up better for your application.
Marine "deep-cycle" batts are more engine starting battery than they are deep-cycle.

 

[Substrate]

Your setup looks reasonable.

Yes it is important to keep the fla's fully charged, but your maintainer looks to have a mild EQ to help take care of the long term stuff. This is unlike the MAJOR fla eq which involves 8 hours at 15.5v CV, a hydrometer, temperature probe etc for the big industrial / monster solar systems.

The "once a week" or perhaps bi-weekly obsession to obtaining 100% charge is more of a concern with SLA batteries like agm's because we can't add water to them to compensate for undercharge walk-down sulfation.

One thing you might want to do which is highly recommended is to *individually* charge each of those batteries before you put them into their final series / parallel configuration for normal use. Maybe separate and do this once a year as kind of a pm.

I don't see any sort of temperature compensation, so if you want to put the cherry on the top, and your solar charge controller or maintainer has temperature comp with a remote "on the battery" sensor, you might want to use that.

But nothing here that you've shown worries me.

 

[Checkthisout]

Draww them down to like 11.5 and then charge them up quickly once every couple months. This will stir up the electrolyte and keep the plates clean.

I would avoid over voltage equalization in lieu of doing the above.

 

[MurphyGuy]

Always keep them fully charged.

You never want to discharge them past 50%. Also, when discharging that deep, it is important to not only get them back on the charger right away, but it is also important that the charger can deliver sufficient amperage to blow the soft sulfates off the plates.

Discharging a battery to 50% and then trickle charging it at low amps (low C-rate) back to full is not good for the battery.

If you put them in storage, I would suggest discharging 20% to 30% or so and then charging them back up to full once a month.

 

[OzSolar]

I can't help but think that golf cart batteries, which are true deep-cycle batteries, would hold up better for your application.
Marine "deep-cycle" batts are more engine starting battery than they are deep-cycle.

No doubt that actual Trojan T105's would be more robust but also much more money. In my experience there's a lot "golf cart" batteries that are closer to marine batteries.

Of course there's a numerous variables but I suspect that in this particular application that the low cost deep cycle marine battery will do fine. IMHO there's a balance of spending extra money for something (capacity and/or resilience) that you'll likely never use vs. spending enough to get what works for 98% of the time.

Other than picking up a refurb T105 from my local battery wholesaler for $45 a while back I haven't priced either one lately so I could be way wrong here.

 

[Vigilant24]

I can't help but think that golf cart batteries, which are true deep-cycle batteries, would hold up better for your application.
Marine "deep-cycle" batts are more engine starting battery than they are deep-cycle.

I believe you are correct and that "true" deep cycle batteries would hold up better than these marine "deep cycle" batteries. I ran across this article that does a good job of examining the differences. In this particular case, though, I'm leaning toward the marine deep cycle batteries even though they probably aren't as durable for long-term cycling. Reasons:
1) Cost: It appears that true deep cycle 12V batteries (e.g. GC12s, etc) cost about $2-$4 per AH. To get my required capacity I'd need to spend $600 to $1200 (Trojans). The marine "deep cycle" batteries (Exide 27MDC) cost about $0.82 per AH, and to get my required capacity will cost about $180. The difference in cost is enough to pay for all my PV panels, and (compared to Trojans) also my inverter and charge controller. If I'd be cycling every day for years, the cost of the good batteries would probably be a worthwhile investment. The weight of the batteries is not significantly different, so I doubt I'm getting 3 times as much lead in the golf cart batteries for the price, but it is certain that their construction (thicker plates held higher off the bottom, etc) is more suitable to hundreds of deep cycles. Honestly, I suspect the difference in price is primarily a result of the "channel" in which they are sold, not the cost to produce them. The marine batteries are commodity items sold in stores with low margins.

2) Surge capacity: It looks like I may need about 7000 watts briefly to start my well pump. Ouch. Maybe the GC12s could do it (300 cranking amps per battery), but the spec sheets don't cover that use and the manufacturers don't condone it. The marine "deep cycle" batteries are rated for about 600 cranking amps each (thinner plates with more area?), so maybe in this use that will come in handy. In a very tough situation even one battery could start the pump and run it briefly (though the pump draw of approx 800 watts wouldn't give me much run time on one battery after Mr Peukert gets his say!)

3) Flexibility: The marine batteries are of a size that I can use in my small travel trailer if needed. In a pinch they can also serve as a starting battery for a car. In this use case (my neighborhood without electricity for awhile), it's hard to know exactly what I might need a battery to do.

If these $200 in batteries can sit quietly on a charger for 4 years or so and then, when needed, give me 200 cycles to 50% DoD over 6 months or so, I'll be perfectly happy to scrap them for for another set.

Anyway, sorry for the long explanation. You make a good point and I didn't want to appear to be dismissing it lightly.

 

[Vigilant24]

The "once a week" or perhaps bi-weekly obsession to obtaining 100% charge is more of a concern with SLA batteries like agm's because we can't add water to them to compensate for undercharge walk-down sulfation.

Thanks. Maybe the low-tech FLA batteries will be an advantage in this case.

One thing you might want to do which is highly recommended is to *individually* charge each of those batteries before you put them into their final series / parallel configuration for normal use. Maybe separate and do this once a year as kind of a pm.

I'm thinking maybe it will be most convenient to keep them separated and on their own chargers all the time. When the lights go out and I need to put them to use, then make sure the voltages are very close and hook them together. I believe I'll probably use them in parallel, at 12V.

I don't see any sort of temperature compensation, so if you want to put the cherry on the top, and your solar charge controller or maintainer has temperature comp with a remote "on the battery" sensor, you might want to use that.

I'm no sure what brand of grid-powered charger/maintainer I'll use in "normal times." The NOCO "Genius" line seems to be recommended by folks in the RV world. This unit (5 amp max) claims to be sufficient for a 120 AH battery, and my batteries would be 110AH. Still, I wonder if the "desulfation" action would be sufficiently robust with a unit this size. It has temperture compensation of a sort, but it appears to be built into the charger rather than a separate probe I could put with the batteries. Better than nothing, but not ideal. I'll keep looking. About $70 each and I'd need two.

But nothing here that you've shown worries me.

Thanks very much for the reply.

 

[Vigilant24]

No doubt that actual Trojan T105's would be more robust but also much more money. In my experience there's a lot "golf cart" batteries that are closer to marine batteries.

Of course there's a numerous variables but I suspect that in this particular application that the low cost deep cycle marine battery will do fine. IMHO there's a balance of spending extra money for something (capacity and/or resilience) that you'll likely never use vs. spending enough to get what works for 98% of the time.

Other than picking up a refurb T105 from my local battery wholesaler for $45 a while back I haven't priced either one lately so I could be way wrong here.

Thanks, OzSolar. I have what appears to be a true industrial battery warehouse store near me, I should go see what they'd charge for two T-105For the reasons I droned on about in Post 8, I think I'll probably go with the "commodity" 12V marine "deep cycle" battery, but maybe they'll surprise me. I expect you are right and that pretty much any SLA will die of calendar age rather than cycles in my use. I sure hope so.

Any thoughts on a good grid-powered battery charger/maintainer for batteries in this use? Would the NOCO "Genius" 5 amp unit (I mentioned in Post 9) do the job for a 110AH battery (one for each battery)?

Thanks again for your input, here and previously.

 

[Vigilant24]

Always keep them fully charged.

I don't want to be pedantic, but if I had enough available charge curent to keep them charged "always," then I wouldn't need batteries . It's good to get them back to 100% as soon as practical, but does permanent degradation occur if that is 12 hours later? 2 weeks later? I'm sure it's a grey area, but it would be useful to have an idea of the impact of delaying the return to full charge.

You never want to discharge them past 50%. Also, when discharging that deep, it is important to not only get them back on the charger right away, but it is also important that the charger can deliver sufficient amperage to blow the soft sulfates off the plates.

When I'm pushing the batteries hard I'll be recharging them with PV solar. I expect to have about 10A of charging current available per battery during the bulk charge phase, so that should get them back to 90% in about 5 hours (of good sun). In your opinion--is that enough to stir things up?
Thanks.

 

[Checkthisout]

Thanks, OzSolar. I have what appears to be a true industrial battery warehouse store near me, I should go see what they'd charge for two T-105For the reasons I droned on about in Post 8, I think I'll probably go with the "commodity" 12V marine "deep cycle" battery, but maybe they'll surprise me. I expect you are right and that pretty much any SLA will die of calendar age rather than cycles in my use. I sure hope so.

Any thoughts on a good grid-powered battery charger/maintainer for batteries in this use? Would the NOCO "Genius" 5 amp unit (I mentioned in Post 9) do the job for a 110AH battery (one for each battery)?

Thanks again for your input, here and previously.

Get marine deep cycle batteries (FLA) and buy an ordinary charger.

You can get an automatic battery charger (black and decker, Schumacher etc) for the same price as those higher amp tenders and they do the exact same thing minus the timed equalization which you don't need.

If you feel the need to have a charger with timed equalization then buy a low amp rv converter and use that. It will be about the same price as two Noco batt tenders and have more amps.

 

[Substrate]

Generally, anything below about 75% SOC aggravates sulfation faster than being above that level. Heat plays a factor. But no magic wand like saying there's a difference at 8.750 hours. Just keep em charged.

A smaller charger like the NOCO 5A, while good, should NOT be used to recover from a deep discharge on those batts. At less than 0.1C, then it is in the "maintainer" category. You could bulk charge with another charger or solar without reaching full charge, and THEN let the Noco do it's thing.

Even though your batts are relatively inexpensive, far too many KILL them by using CHEAP underpowered chargers. No worse than using a $3 wrench for your car you purchase at the glue-tape-scissors rack at your grocery store. I've warned about Schumachers before, best left for DEAD batteries that need recovering, not good batteries needing maintenance

Use a GOOD tool. Noco's are fine. I'd suggest 10A minimum for your size battery to give it a chance to stir, charge, and maintain. The 5A unit won't stir. And will put a superficial surface charge on the batt unless you use it as a "maintainer" when the battery is already near full charge.

My preference is Tecmate-Optimate for maintainers, since I really like their float. (among other things). Unique in that float is on a 30-minute on/off duty cycle. Healthier for float, and reduces the need for exacting temp comp.

I think you get the gist. Now go fill that shopping cart!

 

[ArkCabinMan]

I believe you are correct and that "true" deep cycle batteries would hold up better than these marine "deep cycle" batteries. I ran across this article that does a good job of examining the differences. In this particular case, though, I'm leaning toward the marine deep cycle batteries even though they probably aren't as durable for long-term cycling. Reasons:
1) Cost: It appears that true deep cycle 12V batteries (e.g. GC12s, etc) cost about $2-$4 per AH. To get my required capacity I'd need to spend $600 to $1200 (Trojans). The marine "deep cycle" batteries (Exide 27MDC) cost about $0.82 per AH, and to get my required capacity will cost about $180. The difference in cost is enough to pay for all my PV panels, and (compared to Trojans) also my inverter and charge controller. If I'd be cycling every day for years, the cost of the good batteries would probably be a worthwhile investment. The weight of the batteries is not significantly different, so I doubt I'm getting 3 times as much lead in the golf cart batteries for the price, but it is certain that their construction (thicker plates held higher off the bottom, etc) is more suitable to hundreds of deep cycles. Honestly, I suspect the difference in price is primarily a result of the "channel" in which they are sold, not the cost to produce them. The marine batteries are commodity items sold in stores with low margins.

2) Surge capacity: It looks like I may need about 7000 watts briefly to start my well pump. Ouch. Maybe the GC12s could do it (300 cranking amps per battery), but the spec sheets don't cover that use and the manufacturers don't condone it. The marine "deep cycle" batteries are rated for about 600 cranking amps each (thinner plates with more area?), so maybe in this use that will come in handy. In a very tough situation even one battery could start the pump and run it briefly (though the pump draw of approx 800 watts wouldn't give me much run time on one battery after Mr Peukert gets his say!)

3) Flexibility: The marine batteries are of a size that I can use in my small travel trailer if needed. In a pinch they can also serve as a starting battery for a car. In this use case (my neighborhood without electricity for awhile), it's hard to know exactly what I might need a battery to do.

If these $200 in batteries can sit quietly on a charger for 4 years or so and then, when needed, give me 200 cycles to 50% DoD over 6 months or so, I'll be perfectly happy to scrap them for for another set.

Anyway, sorry for the long explanation. You make a good point and I didn't want to appear to be dismissing it lightly.

Much appreciated, thanks.
Your desire for flexibility is the point which for me makes the most sense in choosing the marine deep-cycle.
I was going to suggest you might consider the 6-volt GC2, which at $240 for a pair, series connected for 12V, makes for a very strong, cost-effective battery as regards the surge capacity you mentioned.

 

[MurphyGuy]

I don't want to be pedantic, but if I had enough available charge curent to keep them charged "always," then I wouldn't need batteries . It's good to get them back to 100% as soon as practical, but does permanent degradation occur if that is 12 hours later? 2 weeks later? I'm sure it's a grey area, but it would be useful to have an idea of the impact of delaying the return to full charge.

Permanent degradation does occur in as little as 12 hours, it actually occurs within minutes, the question is: How much damage? The answer has three variables: 1) The depth of the discharge 2) The amount of time spent in discharge 3) The amount of current used to charge them back up.

Lead acid batteries start the dying process the minute you pour acid into them at the factory. A bit like people in that regard, as soon as you're born, your "time to death" starts ticking away.
And like lead acid batteries, the healthier your lifestyle, the more time you are likely to get.

So yeah, damage occurs in just 12 hours, but you can mitigate that damage by getting them charged back up as quickly as possible.

Lets face it, we buy batteries to store energy.. when it comes to lead acid, the more energy we use from them, the faster they die. So if you can't get the batteries charged back up to full in 12 hours, then it is what it is. Just so you know that damage does occur and it is important to get them charged.

When I'm pushing the batteries hard I'll be recharging them with PV solar. I expect to have about 10A of charging current available per battery during the bulk charge phase, so that should get them back to 90% in about 5 hours (of good sun). In your opinion--is that enough to stir things up?
Thanks.

Actually, no its not fast enough. A 10 amp charge on a 105ah battery that has been drained to 50% is on the far end of the slow side.

For a 105 amp hour battery, you probably want to dump 20 amps into it until it reaches about 80% to 85% SOC, then back off to a 10 amp charge and let it taper down.

In 5 hours, your battery should be fully charged. and if you get it to 90% and the sun goes down and it sits at 90% all night, then you're doing significant permanent damage to them beyond their rated life cycle expectancy. Maybe you don't have a choice? It is what it is, but if you can add more solar charging capacity, then you should do that. It will make the difference between a battery that lasts 5 years and one that lasts 3 or 4 years.

If you are a bit anorexic on the charging amps, a drop-in lithium cell might be a better option. Unlike lead acid, lithium batteries are happiest when they are less than fully charged. And the lower their charge state, the happier they are.

 

[Checkthisout]

Why don't you just buy a jackery or something similar?

 

[Goboatingnow]

Firstly don’t buy anything with “ marine “ on if. ( and I own a boat ). In my opinion buy cheap sealed VRSLA. Do not buy AGMs.

Discharge to 50% max. If you need 80% buy another cheap VRSLA

There’s no issue leaving the recharge to complete over a day or two. This often happens on my boat. Cheap VRSLA are most tolerant oh PSOC ( partial state of charge ) issues then most LA types.

You’ll get 5 years from the battery. Toss it and buy cheap again. ( I use 140 Ah truck tractor batteries )

Don’t ever equalise VRSLA

 

[Substrate]

So yeah, damage occurs in just 12 hours, but you can mitigate that damage by getting them charged back up as quickly as possible.

I do like your recommendation to be more aggressive, because far too often those who buy batteries then cheap out on the back end with the wimpy charging.

But batteries, especially FLA, aren't *that* dainty like eggshells if you don't get them back to 100% after 12 hours of non-use. Nobody would ever leave the house.

You may be conflating the normal process of soft sulfation, which is a natural part of the discharge process - which desulfates when a charge takes place, to that of HARD sulfation, which becomes permanent. And that takes longer than 12 hours, or some other extreme circumstance.

 

[Goboatingnow]

My experience with cheap LA is use then within reasonable limits and don’t over think it.

 

[hyberlut]

Firstly don’t buy anything with “ marine “ on if. ( and I own a boat ). In my opinion buy cheap sealed VRSLA. Do not buy AGMs.

What do you mean by VRSLA? I had to google the term and Wikipedia says that VRSLA (valve regulated sealed lead acid) comes in two different forms: AGM and GEL. So which kind did you buy? GEL is always more expensive and since you said cheap, then I assume you bought AGM...but you said not to buy AGM?? Unless there's another type not mentioned in the wiki entry.