Hi. I have a large lead acid battery bank (12 tubular deep cycle flooded lead acid 12v batteries connected as 48v system). They are fairly new (probably 75 cycles max). Then I decided to switch to lithium iron phosphate with which I'm very happy. However I don't want to get rid of my lead acid batteries. I want to keep them to supplement my lithium iron phosphate batteries when demand is high or for those cloudy days when there isn't enough sun to recharge the lithium batteries. I have tried this and found that on many days the lead acid batteries are not used at all (stay at 100% soc) and on some days they get used down to 95 or 90 % soc. Rarely, they get used a bit more heavily and go down to 80% soc. So the lead acid batteries are either not used at all or very lightly cycled. Whenever used they get recharged back to 100% soc within 12 hours max. My question is: with the way I'm using my lead acid batteries, will they last for a VERY long time since they are being cycled so lightly (a long time in calendar days/years)? Or is such light use detrimental to the batteries in some way? I mean if I calculate their cycle life with these shallow and infrequent cycles then theoretically they should last for many years (as long if not longer than the lithium iron phosphate batteries which are doing most of the work on a daily basis).. right? Or am I missing something? Do lead acid batteries degrade with time whether used or not (calendar degradation)? If so, then cycling the lead acid batteries so lightly is actually wasting these batteries which I could be working harder and preserving my lithium iron phosphate batteries by cycling them less. Any info on this topic would be appreciated. Thank you.
Flooded lead acid battery life if not used
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peakbagger
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Are you using desulphinators on the FLAs?. Power plants have large banks of FLAs to run the turbine oil cooling pumps, switchgear and other shutdown loads on loss of power. I expect a home solar person would drool over the banks 
In many cases I saw desulphinators used. I have heard of but not seen that large submarine type batteries have electrolyte circulation pumps to circulate the electrolyte for the same reason.
In many cases I saw desulphinators used. I have heard of but not seen that large submarine type batteries have electrolyte circulation pumps to circulate the electrolyte for the same reason.
Depending on their design some lead acid batteries are impacted by keeping fully charged and only lightly discharged. Based on the chemistry involved batteries naturally breakdown given time. Even with the best of usage a battery eventually dies. Proper charge discharge can improve how long a battery lasts but it can not overcome natural chemical processes.
Bit like us. You can eat right, sleep right, exercise routinely and reach your bodies natural lifespan. Or you can mistreat your body and shorten it considerably.
Bit like us. You can eat right, sleep right, exercise routinely and reach your bodies natural lifespan. Or you can mistreat your body and shorten it considerably.
OzSolar
Whatever you did, that's what you planned.
I suggest finding every bit of factory documentation on your battery and following those instructions precisely. If you do that I bet you can get 20+ years out of them.
Batteries have both a cycle life and a chemical life (my term). At some point age will get them. In fact most batteries I've been around died of age and abuse long before cycle life. (I've been dabbling in off grid power systems for just over 3 decades.)
Telecom types of batteries optimized for decades of shelf life but trade deeper cycles for that. Starting batteries deliver many amps but trade deep cycles for that. (just in case you didn't know. ha).
Most sulphation happens when batteries are left at a partial state of charge.
Batteries have both a cycle life and a chemical life (my term). At some point age will get them. In fact most batteries I've been around died of age and abuse long before cycle life. (I've been dabbling in off grid power systems for just over 3 decades.)
Telecom types of batteries optimized for decades of shelf life but trade deeper cycles for that. Starting batteries deliver many amps but trade deep cycles for that. (just in case you didn't know. ha).
Most sulphation happens when batteries are left at a partial state of charge.
12VoltInstalls
life passes by too quickly to not live in freedom
I would keep the electrolyte levels maintained and maybe every 6 months run them two or three days to 55-60% charged and recharge the next morning; then run an equalize cycle for an hour or so. I think this will possibly let your batteries last the aforementioned 20 years extended life with your minimal cycling. Imho- I’m no scientist.
I saw some (military communications 30+ years ago) FLA on a rack with clear plastic cases. The top was a cover, terminal holder, plate mount, etc. They could just lift the top, plates and all, out of the electrolyte bath and rebuild/repair. I was sort of taken with that design and it looked nice.Are you using desulphinators on the FLAs?. Power plants have large banks of FLAs to run the turbine oil cooling pumps, switchgear and other shutdown loads on loss of power. I expect a home solar person would drool over the banks
peakbagger
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Of course, buy some very inefficient and thirsty Nickel Iron batteries and they will last "forever"
Unless they are really well designed batteries 20 years is just about impossible. However your advice for maintenance is sound.
OzSolar
Whatever you did, that's what you planned.
I got 23 years out of my Rolls Surrettes.
OzSolar
Whatever you did, that's what you planned.
That's the truth. Something like 60% or less round trip efficiency and 20% monthly self discharge if I remember correctly.
That is excellent lifetime. Good LA batteries cost a lot. Heavier lead plates, better separators, room for shedded material to settle at bottom of battery case before reaching a level to short out and the like.
If you could find them LA batteries designed for naval submarines were incredibly overbuilt.
peakbagger
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Incredibly overbuilt and vastly oversized for a typical home system. They do come up for sale on very rare occasions but I think the US Navy required they be directly recycled
12VoltInstalls
life passes by too quickly to not live in freedom
You could be correct but I do know a couple of people offgrid with not-commodity lead acid batteries. One woman with a bunch of humongous 6Vs wired 12V got 12 years out of them cycling them for daily use. Had a generator for the cloudy months. Telco batteries used to go long pretty well, too.
Lead acid battery design is an interesting area. Big problem I see these days is the low quality of lead being used in many of the batteries available. Recycled lead can have impurities in it that allows for more rapid degradation. The Far East and China where most lead acid batteries are made these days have very lack standards.
Used to be automotive batteries could be relied upon to go for 8-10 years. Nowadays you really should replace it in the 3-5 year range. Some of that is increased demand modern autos have but a lot of it is bad build quality.
Risky Rob
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Do you charge and discharge LiFePO4 and lead acid batteries together, or do you switch between banks?
peakbagger
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BTW, If you want a "forever battery" I expect these submarine batteries will work https://www.ebay.com/itm/3019412998...rentrq:499d71c51820a764ad831e0fffff6de8|iid:1
Kind of a steep entry price (the price doesnt include acid). Probably need a small gas turbine from an Abrams tank to equalize the bank.
Kind of a steep entry price
(the price doesnt include acid). Probably need a small gas turbine from an Abrams tank to equalize the bank.
Risky Rob
Solar Enthusiast
Wow, $4353.00 for a 2V battery. I would need 12!?BTW, If you want a "forever battery" I expect these submarine batteries will work https://www.ebay.com/itm/301941299859?_trkparms=amclksrc=ITM&aid=111001&algo=REC.SEED&ao=1&asc=20160908105057&meid=a3202f7a3d1846269b8a48fab35df43e&pid=100675&rk=1&rkt=15&sd=301941299859&itm=301941299859&pmt=0&noa=1&pg=2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci:a9c3a753-0f2d-11ed-8428-96bf629a7f78|parentrq:499d71c51820a764ad831e0fffff6de8|iid:1
Kind of a steep entry price
The entry price ain't bad for a 50+ year battery that only the government is normally allowed to buy. Bit out of my price range for the "A" cells but it would be interesting what they want for the "C" cells.BTW, If you want a "forever battery" I expect these submarine batteries will work https://www.ebay.com/itm/301941299859?_trkparms=amclksrc=ITM&aid=111001&algo=REC.SEED&ao=1&asc=20160908105057&meid=a3202f7a3d1846269b8a48fab35df43e&pid=100675&rk=1&rkt=15&sd=301941299859&itm=301941299859&pmt=0&noa=1&pg=2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci:a9c3a753-0f2d-11ed-8428-96bf629a7f78|parentrq:499d71c51820a764ad831e0fffff6de8|iid:1
Kind of a steep entry price
Some billionaire or super villain will probably buy them to outfit their Bat cave or secret under volcano lair.
Risky Rob
Solar Enthusiast
Aliexpress has them for $299 plus free shipping via Hong Kong Air.
??
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