A project that has been going on for at least half of April has been my semi-annual testing of various batteries around the house. Primarily, not the stuff I use regularly, but stand by batteries for after a hurricane or other extended power outage. As usual, some of them were fine and a couple others weren't. It's a topic I've written on many times.
The "problem child" this time around was pictured in a post from December 2015, and the battery has a label on it with the date 1/5/14 so it was nearly 2 years old in '15. That battery has been getting lower and lower in capacity for years and it's finally time to say good bye and send it off to the recycling center. A year ago that 35 Amp*Hour battery delivered 10 AH. Clearly not good, but a thought that has to be addressed is "how good does it have to be?" If I'm running things that don't take much current, and that can be used longer with the 10AH battery, why not keep it? Even or especially if it's a "backup to a backup."
This time around, that battery hasn't been able to deliver more than 3 AH. That's approaching practically worthless. It's also just over 10 years old now, so that's yet another sign that it's past time to set it out to pasture.
My battery farm contains three Lithium-Ion car jump starting batteries (like this but not this one) that were chosen because they have USB outputs that can charge a phone or run anything that uses USB power, and they also have 12V outputs. Next, I have that dead AGM battery, and two more sealed lead-acid batteries I recovered from my old UPS that died last October. Then there are a few Ryobi "One +" 18 V batteries primarily for the tools that take down (and put up) hurricane shutters and all, and finally a few 18650 cells that were bought as an experiment, for no particular application.
In the decade since I bought that AGM battery, a "new hotness" has made tremendous inroads in home use, coming down steeply in price and becoming more widely available. These are Lithium Iron Phosphate batteries, usually designated LiFePO4 (or LiFePO4) and called by a handful of other names. I've had tendency to call these Life-po, with the first syllable being the word "life" and the last is pronounced "po" with a long "o". I maybe the only person on Earth using that.
As class of batteries, LiFePO4 batteries have a substantial number of
advantages over lead acid and AGM (really just another type of lead acid - adsorbed glass
mat). This illustration taken from
a product listing on Amazon
is a good summary. The only thing lead-acid batteries might be better at is a
lower starting price.
Let me be go all disclaimer. This isn't any sort of endorsement of Eco-Worthy batteries or this specific one, but it's correct to the best of my knowledge and convenient to post here. I haven't bought this or any other LiFePO4 battery. Somewhere in the last year or two, I think I heard they were a good brand, but I have nothing to base that on.
An important point is that specification second from the bottom: Depth of
Discharge (DOD). The exact number for what a lead-acid battery can discharge
to depends on what kind it is; starting batteries are different from deep
cycle batteries, which are different from sealed lead-acid (SLA) or AGM.
Still, the best they do is to around 60% DOD - which says that 40% of the capacity is unusable. That says that if my 35AH AGM
battery was really delivering 35AH, I could discharge it to 14AH (40%) using
21AH, or perhaps 17.5 AH (50%) using the same. That 30AH LiFePO4 battery would give me much
more - even if I stopped using it at 90% discharged, that's 27AH. Instead of this pictured 30AH battery, I'd get the same amount of usable AH as the AGM gives with a LiFePO4 half that size.
Most (if not all) of the Life-PO batteries have a battery management system built in which I believe means none of my lead acid battery chargers will work with one. The cars still have lead acid starting batteries, so I'll keep one of those chargers around. Switching over to the new battery chemistry brings up all sorts of questions, so I'm digging for information. With pretty much 30 days to the start of what looks to be an active hurricane season, I need to get moving fast.
Thoughts, recommendations or sick jokes are welcome from those of you familiar with these things.