Battery storage issue

[Jonathan Pierce]

To begin with, I should explain that my knowledge of solar power is limited but, out of necessity, I am trying to learn. Four years ago my wife and I purchased a small farm in Costa Rica, off-grid of course, with a rudimentary solar system. The system was old and poorly maintained so we replaced it with a system composed of 12 Perlight 330W panels, two Outback Flex charge controllers (reused from previous system) one 60a and one 80a, 16 Trojan T-105 6v batteries in two banks (48v system) and a Studer Innotec 4 kw inverter. The system worked just fine for well over a year until at least March 2020 (yes, we had to scurry home to Canada!) I did not see the system, or Costa Rica for that matter, for the next 20 months. We have people looking after the place when we are not there and one of the jobs of our manager is to regularly water the batteries. There is no real power usage when we are not present, maybe a light bulb or two at night but that is about it, so the system was sitting without cycling and fully charged for 20 months. When we returned in November 2019, the system ran out of power the second night and would not provide power through the night for the next two weeks. I blamed the batteries (SG readings were in the 1.10-1.12 range), thought that bad maintenance had ruined them, and probably would have ordered a new bank if anything other than Chinese batteries were available. The outfit that installed the new system was willing to sell me more batteries but that was about it, they've pretty much abandoned us. After two weeks the capacity of the batteries had improved enough that we had power through the night (mostly a refrigerator). We went home in early December and after another COVID delay, returned this last March. Same thing happened. After about 3 weeks, the bank would run through the night and having enough power was never an issue. The SG readings by April were in the 1.28 - 1.30 range. So I think I should be happy that maybe I don't need to replace the batteries, but I'm still not sure what the problem is and whether it will happen again when we return in the fall. I have just spent the last day or so reading the manuals for the Outback charge controller, the Trojan information and Rob's article on battery maintenance and now understand what the words absorbing, floating, zzz, mean when I see them on the controllers. I will check the settings on the charge controllers when I return. I have a generator that could be used to charge the batteries if necessary.

Long story, but I'm hoping someone might be able to point me in the right direction.

[Rob Beckers]

Hi Jonathan,

Sounds like you did the right things!
What I suspect happened is that the batteries slowly but surely sulphated over time, leading to less capacity (where there's lead-sulphate on the plates that section no longer participates in the chemical reactions). Getting back and properly charging the batteries, with some cycling, slowly reversed that sulphate back to lead (negative plates) and lead-oxide (positive plates) and you're back where you started before you left.

Two things: SG values of 1.280 and up are really too high and will cut into the life expectancy of the batteries. Ideally aim for 1.265 - 1.270 after a full charge. In your case I would downward adjust the absorb time so it gets more into that range.

Second one is that T-105 batteries are made to be 4 - 6 year batteries with good care. They are not very long lasting. Trojan makes another line, and the equivalent type for the T-105 would be their SPRE 06 255, those are designed to last about 10 years. If you can get Rolls, their S-550 batteries (now named S6 L16-HC but nobody can remember those new type codes) are good for 10 - 12 years with decent care.

-RoB-

[Jonathan Pierce]

Thanks Rob. I was hoping that this would be your response. The T 105s that I have are labelled as solar batteries and the system description does describe them as T 105 RE. I will pick up one of your suggested Swiss hydrometers as I'm not sure about the one I have been using. But I will change the charge controller settings as you suggest. When this battery bank is finished I think I can get Rolls batteries in Costa Rica. Hopefully it will still be a few years and by then lithium might be more approachable in terms of cost. One last question, if my batteries are slumbering in the fall would it help to give them a jolt either by running an equalization or by charging with a generator (I think I can hook up my generator through the Studer inverter)?

[Joe Blake]

Hi Rob, Jonathon

"Second one is that T-105 batteries are made to be 4 - 6 year batteries with good care."

I'd have to disagree with you (or maybe Trojan) to a certain extent, Rob. I've got a "stand-alone" system which uses folding 12 volt solar panels and 4 x T105 batteries configured series/ parallel to store the power, and a series of small individual inverters ranging from 150 Watts to 600 Watts. I assembled it in 2004 and I replaced the T105's in Nov 2013, due to neglect on my part, allowing them to overheat and dry. The replacements are still giving stirling service (May 2022), and look like soldiering on for a while yet. I can recommend them.

[Rob Beckers]

Jonathan, the T-105RE line is indeed a better battery vs. the regular T-105. We used to sell those, and in a way still do, Trojan renamed this line to SPRE 06 255, they are 10-year design life batteries.

As long as you're cycling lead-acid batteries they should get a full 100% recharge every 2 to 4 weeks. Without that the lead-sulphate crystals on the plates keep growing to the point where they become hard or impossible to reverse. In effect that leads to (permanent) capacity loss. We've found them more forgiving when they are just 'sitting' (no cycling, no current draw, no charging); If put away with a full charge (ie. SG at 1.265) they're quite happy to sit for 5 or 6 months, the SG values will slowly drop (self-discharge) but they are pretty easy to revive again with a full charge. My non-scientific theory is that this only grows small lead-sulphate crystals that easily reverse back.

So, regarding your question, it depends what you do with your batteries in fall. If they are still being used it would be good to periodically get a 100% (SG at 1.265) charging back in them. If they're just sitting idle with nothing connected then you can let them sit.

Joe, I can only congratulate you on the long battery life! I do hear stories similar to yours pretty regularly, so batteries can live past their design life. I also see lots of cases of people killing them prematurely (more often than the "long life" stories unfortunately).

Regular T-105s are designed as golf-cart batteries meant for 4 - 6 years of service. The manufacturer makes the plates just thick enough, with just enough lead-oxide paste on the positive plates, to reasonably get to that time with decent care. Even when batteries are not used at all but sit at float all the time they still age, plates corrode, and shed active material, such that generally at the end of their design life they have (much) less capacity. I can see that local conditions, and care, will make a difference how fast they 'age', and another big factor is how much capacity you need: Lots of people never cycle past 10 - 15% and when they say "I got 20 years out of those 10-year batteries" they ignore that the battery capacity may be down to just a fraction of what it was when new, but it's enough for them to make it work.

-RoB-