diy solar

diy solar

Good, affordable, quality batteries...

SolarRat

Solar Addict
Joined
Oct 3, 2019
Messages
981
Location
Southwest Florida
I see too many people getting into this "hobby" and thinking they must use these high priced and sometimes questionable quality lithium batteries, ordering from who knows who from who knows where. For decades the off-grid, marine and RV crowd have gotten by just fine with FLA's.

Mass produced LifePo's are still in early stages with many shady players. In 5 years the prices will come way down and the good players will rise to the top as the low quality junk gets weeded out. I think using good lead acids that will last until that happens makes good sense.

I can recommend these for those who just want a lot of storage for as little $ as possible. They are made by East Penn (one of the big three batt manufacturers) and are sold under many labels including Duracell Ultra Deep Cycle (for more $$). They are true deep cycles and have been used for years with good reviews. I use them for trolling motor batteries, and many people use them for RV and off-grid battery banks. They are 12v and 105ah (some say 115ah) so each battery holds 1260 watt hours. 4 of these batteries will cost only $400, can be configured in 12, 24 or 48v and will hold 5kwh! I don't think you can beat them watt per $ for new batteries.

 
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To avoid confusion, the batteries above are lead acid, not lithium. Where did you find the 105Ah rating? Most batteries that size are around 50-55Ah. It's not specifically stated in the specs, and there is no direct translation from CCA to Ah.

It should be noted, and part of anyone's consideration, that you really only get half the rated watt hours if you want the batteries to last, which means staying above 50% SoC. Doesn't mean you can't discharge further, just means you are shortening the battery life overall.

I had the same considerations when buying my first solar battery. I went with an AGM lead acid 100Ah. Works fine for my application.
 
I was just like SolarRat described. I was nearly ready to pull the trigger on some LiFePo4's but then I decided I have a lot to learn first and should cut my teeth on an AGM (certain kind of lead acid) battery first. I got this one and so far been very happy with it. I have not put much load on it yet because I accidentally got the wrong inverter, but will soon.
 
... Where did you find the 105Ah rating? Most batteries that size are around 50-55Ah ...

It's rated on most websites, just not O'reilly's for some reason. I've tested the capacity many times on my boat, and usually draw 600w out of it for a 50% DOD...and the battery still reads 12.3. In the past I have had to almost fully drain the battery to get home in emergencies, and it exceeded 1200wh.
 
I have a couple of AGMs that are rated at 120ah and weigh about 30kg a piece. The weight of that battery is in the area I'd expect for a 105ah battery.
 
It should be noted, and part of anyone's consideration, that you really only get half the rated watt hours if you want the batteries to last, which means staying above 50% SoC. Doesn't mean you can't discharge further, just means you are shortening the battery life overall.

That is very true, but can also be a little misleading. Sure, the lower you take the cells the less charge cycles they will last. Keep it to a 30% DoD and it may last 2000 cycles, but if you always take it down to 80% you may only get 200 good cycles. If your use calls for daily cycling, like in an off grid house, keeping it to 50% depth of discharge is extremely important. BUT...for back-up power, an RV, or a cabin in the woods that only gets used once a month?...you can draw it down much more.

Properly maintained and kept at a safe DoD, these batteries can last 10 years in a perfect world. There are many accounts of this happening. But 5 years is much more realistic due to calendar aging, no matter how well it was taken care of. So let's say these batteries should last 5 years.

Over 5 years, 200 cycles works out to be 40 cycles per year at a 80% DoD. If you only use that cabin in the woods, or RV, or boat, or backup power a few times a month, taking your battery lower than 50% is not such a big deal. It's all about the application.

Back when I tournament bass fished, we'd be on the water at least 100 long days a year. We had 3 of these batteries onboard, one on the front trolling motor, one on the rear troller, and one (usually an older one) as a spare to get us back to the ramp when the first two died. We had no idea about DoD this and life cycles that. We'd run them down till the boat no longer moved, then hooked up the spare to get us home. We'd get many years out of those abused batteries, and at least 300 cycles. Going easier on those batteries probably wouldn't have added much calander life to them, but would have required more batteries, weight and money.

I think heat is a bigger enemy than discharge level, but that's another topic....

TL;DR: The guy who just wants batteries for an occasional grid outage does not need 5000 or even 500 charge cycles, and can get much more than 50% out of a flooded lead acid battery without sacrificing much in the way of calendar life.
 
Sure, the lower you take the cells the less charge cycles they will last. Keep it to a 30% DoD and it may last 2000 cycles, but if you always take it down to 80% you may only get 200 good cycles.
Is this also true for Lithium and NiMH batteries used in smaller consumer electronics? That may be why my rechargeable AA's don't last too long as I discharge them down to about 20% every time. I might get 40 charges out of them.
 
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Affordable is a relative term. I paid $620 for my 100ah lithium and that didn't cause me financial ruin. And I will get 10 or more years use from it. $62 a year.
 
Affordable is a relative term
Indeed if you calculate the calendar life of li ion or lifepo4 with the cycle life in terms of how many times you will do a full cycle a day.
Throw in your kwh price from the grid compared to a gasoline operated car or your household daily consumption relative to heating/cooking to get rid of gas/wood..ect
 
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