For the last year I’ve been researching a grid tied solar electric system with batteries for night and backup. Overall solar is affordable but the battery cost, nope, batteries will almost double the cost. I did find these awesome lithium batteries on ebay, they’re 12V and 40 amp hour, two of these in parallel would be fantastic. You can find them as cheap as $150 a battery. They’re used BUT a solar guru on YouTube tested two random ones and they were still above %90 capacity. Some batteries when you buy them brand new don’t have %90 capacity. the batteries are called Valence, they’re used in medical devices.
Lithium units have great performance, but personally I can't justify the expense for weekend warrior use like I currently do. If you had a specific high performance need for full-time live-in boondock operations, maybe. I haven't run the numbers, but my gut tells me it's less expensive to invest in more solar panels, and use wet cell or even AGM batteries, than it is to go lithium at this time. That's pretty cool that there are some used lithium batteries out there. Might allow for some experimentation. Thanks for sharing it!
Keep in mind you stated the pair will give 40 AMP HRs of which 20 can be used. I would do and energy audit first. A Group 24 wet cell will give more AMP HRs
Oh I realize these are not perfect. 80 amp hours, 2 40amp hour batteries in parallel, this would be much less capacity then I currently have. However per kWh these lithium batteries are actually cheaper compared to cheap wet cell batteries. Currently I have 2 group 31 which give me 240 amp hours. However, this is way more capacity then I need. I’ve been on 5 day boomdocking trips and only used about %30 capacity. This is from my Victron battery monitor. I believe I paid $250 for EACH of my group 31 SLA batteries. So $500 total. I could get 4 of these lithium batteries for that price. 4 in parallel would give me 160 amp hours. That’s plenty.
If they have a good BMS installed you can draw these batteries down to 10% with no damage and they actually like this. I have a 125 ah Torque 12v battery that has a internal BMS and it is a drop in battery. It actually has a top ah charge of 136 after charge is complete. I have 750 watts of 24v solar and a li40 renogy MPPT controller if I use 50% over night it will be back at full in about 2.5 hours.
It does have an internal BMS, and when the batteries are connected through the attached cables the batteries talk to each other and will balance properly.
Thought about it, but can't justify the cost. I run one Duracell Group 31 flooded battery with 105AH. After three nights we barely put a dent in it's capacity.
You don't apply the 50% "rule" (which is garbage in our application anyway) to lithium batteries. Use the 90% rule for lithiums.
Group 31 Deep cycle FLAs are $80 at Sam's on sale and $100 regularly. There is no reason to pay much more than that for batteries. Unless there are weight or size considerations, there is no reason to go with lithium at this point, there are much more cost effective options out there.
Even using the 90% rule and at $150 per battery wet cells will out preform when comparing amp hrs. to cost. Remember these are just 40 amp batteries.
Definitely. Agreed. Nothing will beat a flooded lead acid battery for AH/$. I was speaking to the 50% rule "accepted without any analysis" trope.
For you perhaps but many others of us have moved on to AGM and would never go back to flooded despite the higher cost of a sealed, maintenance free battery.
Brother (TT) went from marine to AGM to Li in 3 years. I showed up with portable solar panels and his G24 and Odyssey were @ 11.8v. He went to 4 100ah AGM and all was fine with 300w roof top solar. Decided 3 Li battle borns was the way to go! Still fine. With my new to me trailer with hydraulic lift, a dual post G24 fits nicely. took a week + with various chargers to get a decent hydrometer reading.
I think when my SLA batteries are toast I'll be picking two of these lithium batteries up. Weight is a lot less, and my tongue weight is already up there with my E3. Plus I can run these way down and not worry about damaging the battery. Also a lot smaller so I will be able to fab up a nice compact battery box. To each their own. In the mean time I wont complain about my SLA deep cycle batteries, they do everything I need, just take up a lot of space on my toy deck.
We use Li-Ion batteries in some of our products. Since I was documenting the charging system, I had to do a whole bunch of reading about them. Learned a whole bunch of stuff. They're definitely temperature-sensitive.
