I have replaced my GC-2 golf cart batteries, too.

I went with SOK LiFePO4. They have a 24 volt 100 amp-hr battery. Their case is steel and the top is held on with 12 screws. It is serviceable if ever needed. The BMS is built in and has low and high temperature disconnect. Also a low voltage disconnect. 55 lbs. 7 year warranty. $1011 delivered, each.

I ordered 2. One is lost in shipping though. I have charged it to 90% at home with my faithful Iota DLS27-25 charger that I bought back when I put the original system together. All I needed was the new IQ4 Lifepo plugin module. $20. There is a bluetooth app for monitoring. The second will be paralleled when it comes.

I installed the one battery today and reprogrammed the Midnite Solar Kid controller. It works fine. I may move them inside. There is a suitable space inside the other side of the wall where the battery cabinet is located. Two 30 to 36" cables should work. Then the existing cabinet can be repurposed for storage.

After removing the old lead-acid batteries I washed the battery cabinet out with some baking soda and water to neutralize whatever acid was present. It bubbled a little. The 5 year old GC-2's are being donated; 4 to each of two young neighbors.

A very nice bonus that comes with LFP batteries is the faster charge. Less internal battery resistance = faster charging grom the same PV array and charge controller.

very nice....

Cool!  I'm finding that the 240AH I am using of my 360 (still gotta balance that last one) is MORE than the 660ah I had before by a long shot   and I can see much better performance this winter when there is less sun which means less generator run time

I'm stoked!  Heck, I need to get back up and work on that soon!

Today is very cloudy. We've not seen blue shy since yesterday. For a few hours early this morning we were in a cloud. (8800 ft altitude).

The LFP lithium battery is recharging. Not real fast but much better than the lead-acid batteries would do under similar conditions.

Nice!  I do find they recharge much faster!

 If you go with lower charge rates, this increases charge time, and if you have batteries in parallel, having a bit higher rate gives you more time for the absorb cycle to balance the bank, especially if it's an open-loop comms system.   If open-loop and you have 2, 3, or 4 parallel strings, the longer 30-60 mins absorb timers allow for better balancing between the parallel strings. Might be a good thing to shut down a string or 2 of PV once in a while for better balance.

Sorry to hear about Glen. Appreciate the update Don.

Quote from: Dave Sparks on August 27, 2023, 01:37:32 PM If you go with lower charge rates, this increases charge time, and if you have batteries in parallel, having a bit higher rate gives you more time for the absorb cycle to balance the bank, especially if it's an open-loop comms system.  If open-loop and you have 2, 3, or 4 parallel strings, the longer 30-60 mins absorb timers allow for better balancing between the parallel strings. Might be a good thing to shut down a string or 2 of PV once in a while for better balance.

Sorry to hear about Glen. Appreciate the update Don.

Hmmm.....

So the batt co tells me to set the Charge Controllers at a specific voltage with no absorb or float time difference (same voltages) because the BOM's manage the batteries anyway.  

I'm not sure, and will find out next week I think, but I'm thinking my batteries are finally balanced as I saw them all accepting almost the same amperages when I kicked on my generator though they were not the same and that confused me.

I need to hook up my LiFePo4 battery charger so I can use it separately and disco the batteries so I can see if they are, indeed balanced and if not, charge up the 1 or 2 that aren't.

I'm running 3 24v batteries in parallel (FYI)

This is probably not an original thought, but has any system of multiple batteries been hooked up .. not in hard-wired parallel .. but in parallel only in orientation, and by using switching relays .. only one battery is in circuit at a time?  By proper measurements and controlling, all batteries would see similar loading and charging.  An additional up front investment, but it works around the problem of batteries not matching exactly .. at least, I would think.

The missing second battery of mine never showed up. The tracking number shows it should be in a shipping terminal but it evaporated or something. In the interim I have been using the one and have been quite pleased with its performance. For the time being I have asked the seller to refund the cost of the missing battery and they agreed.

One battery, no parallel connections, is very nicely simple. So far we have never discharged to less than 78% charge left. That is partly due to the  ability of the LFP battery to recharge after the noontime power use to be fully charged again by dinner time. It also helps that we now have a longer exposure to sunshine than before. A small silver lining from the wildfire destruction of so many 70 foot pine trees.

Batteries in parallel are, I believe, vastly superior to those in series. Sitting idle they should, in theory, self equalize to the same voltage. The BMS in each battery should, in theory, match each cell in the battery to within very small variation. The cells in our 1 battery are extremely close in voltage, measured in hundredths of a volt. My memory is not as good as it once was and the log is at the cabin and I am not.

If the less sunny parts of the year prove to make a second battery useful I will add a second. But we don't snowshoe in, in winter anymore and our power use has diminished with led this and that. So, we shall see.

Don, are your batteries in a warm environment?  Have heaters?

I'm in a bit of a panic as Big Battery told me to get my batteries into a warmer space ASAP as we're likely going to see minus temps at the cabin later this week (as in two days)....seems anything below 23F isn't good for them but if they are warmed to over freezing that day they should be fine...but if they aren't and they drop even colder I'm told they could be damaged (cell damage) and after $3600 investment I'm going to be driving back shortly to move them into the back room!!!

Our SOK battery is inside the cabin, but unheated when we are absent.

The spec sheet for my SOK battery states that it can be...
... stored -22F to 95 F
... discharged -4 F to 140 F
... charged between 32 and 113 F

So I hope SOK is correct on that. Their temperatures pretty much match the data I collected before buying the SOK. I had been considering building the battery myself with LFP prismatic cells (the rectangular things) and a BMS board. Building a case for them and so on. I collected data on three different name brands of cells.

We seldom see any temperatures below zero or over 95 F.

Best of luck

Interesting.

I had conflicting information on mine as it states they can discharge down to -22F but storage is +23F

When I asked about this I was told they can discharge much lower than storage temps but it isn't always good and the cells can get damaged at those low temps.

Here's what BigBattery says about mine:

Turns out that is an error -- it should be -4 not -22