Battery bank problems

[serialteg]

Hello,

I have a problem.

This is my first solar system, first battery set (four T105's, 6V, 24V series). I've been using it for about two years as a power backup system to the grid (failure).

I wired two batteries in my bank with the wrong AWG size cables (I have since wired the whole bank and inverter cables to 2/0AWG THHN welding cable).

The negative pole to the inverter cable was 0AWG, and positive to negative was 0AWG as well. But then for some unknown reason I used a 4AWG to connect tha battery's positive pole to the next one, and that one developed a bad middle cell, that didn't rise over 1.250 in specific gravity on a normal charge when the rest of the bank (and the two other cells in the battery) reached 1.275. The two other cells on this battery behave normally.

The next battery I believe had a 0AWG cable as well connecting it to the bad one, but the positive cable going to the inverter was not 0AWG, it was thinner. I don't remember the AWG.

I was told by a friend this next battery would be the one to start failing, and soon enough it did. I was foolish enough to not change the wires then. This battery, the one with the positive cable to the inverter connected to it, eventually started dropping SG on every cell. Now while the two remaining good batteries go up to 1.300+ SG on an equalization, these two questionable or "bad" batteries don't rise over 1.275-1.280 (at EQ), at which point I ended EQ.

After normal nocturnal use (discharge - I usually do a 30% DOD, about 1.6kw), my "good" batteries go down to 1.250 (all six cells, both batteries), but the questionable cells on the other two batteries vary between 1.225 and 1.210.

For example, on today's charge, my two "good" batteries reached 1.275, whereas the two batteries I very likely killed reach 1.250 in the best cells of the bad bunch, to 1.230 maybe in the worst.

Now. I've been reading on the forum and asking around, and I already know it's a bad idea to add new batteries to an existing battery bank (replacing the two "bad" batteries). So does this mean that I can pretty much throw all of this battery bank in the trash?

I have also since read that it's a bad idea to add a parallel new bank of batteries and still using this one.

So does that mean I'm SOL and have to throw the bank away?

As money is a factor, should I continue to use this bank until all its batteries go bad, however long that may be?

PD. As an ending question, when factoring in the DC amp loads running thu my batteries, do I have to add the house amp draw to the power coming in to the batteries from the controller?

[Mike90250]

Fortunately, your friend is WRONG about the wires causing the battery to die. Since they seem to be wired in series, all points of the circuit, see the same charge/discharge amps. What's likely happening is just bad luck about the battery lifetime. Even the best batteries eventually die.

What was the warranty for the batteries ? If you got 50% of that, you are doing good.

[serialteg]

Fortunately, your friend is WRONG about the wires causing the battery to die. Since they seem to be wired in series, all points of the circuit, see the same charge/discharge amps. What's likely happening is just bad luck about the battery lifetime. Even the best batteries eventually die.

What was the warranty for the batteries ? If you got 50% of that, you are doing good.

T105 is only 12 months warranty.

Actually my friend didn't refer to the cables as the cause, that's on me. He was referring to the bad cell on that battery. That the battery after that one would develop bad cells also. His family had a FLA battery business, so I think that's why he thought of that.

I was the one who was thinking that the cables were the culprit. It seems to me that amperage wouldn't be distributed equally - that a bottleneck would form on the 4awg if the loads were over 60 amps DC @ 24V, and on the positive terminal to the inverter as well, which were both the batteries that had such cables connected. That's why I wanted to know if my amp draw sums to the charge applied to the batteries as the total amps running thru the battery bank cables.

So in this case, what would you do? I already have the bank properly wired (I hope lol). But as things stand now?

Keep on using the bank until it fails, and have another bank ready to go side by side? I mentioned money as an issue, but I live in Puerto Rico, and hurricane season is about to start.

[Mike90250]

The good thing was the batteries were wired in series. The different (smaller) wires would limit current flow a bit, maybe cause the inverter to fault from undervoltage.

With the wire size corrected, all you need are 4 new batteries. You got twice the design life out of them, consider the other batteries about ready to loose a cell and die too.

Golf cart GC2 batteries may be less expensive than T105 but they are lower ( 180ah ) capacity too. With your usage, they may last 1 year. But the storms are coming, and you know the existing batteries are all on borrowed time.

There are also "Floor Sweeper" L-16 batteries. It all depends on what you can get locally at the best price.

[serialteg]

1,200 cycles @ 50% DOD for T105, 2,000 at 30%. I should've gotten way more life out them, since I don't cycle daily that often - maybe 100 cycles in a year, since I mostly use the grid, and these batteries are mostly on float, in standby for power outages.

But oh well. Thanks for your help always, Mike. You're a staple thru the years here