When I went shopping for new batteries to replace worn 7AH sealed lead-acid (SLA) batteries in my APC uninterruptible power supply (UPS), I saw listings for an interesting alternative: Lithium-iron phosphate batteries (LiFePO4 or LFP) packaged in the 7AH SLA form factor with a built-in battery protection circuit, advertised to be drop-in upgrades for systems designed to run on SLA batteries. They offer many advantages and cost more but, if they last longer, there's a chance LFP batteries would be more economical long term. I thought it was worth a try and ordered a two-pack from the lowest Amazon bidder of the day. (*)

Here is the "before" picture, my worn APC RBC cartridge and the two 7AH SLA form factor LFP batteries I intend to upgrade to.

The APC cartridge is held together by front and rear sheets of adhesive-backed plastic. This unit didn't peel as cleanly as the last time I did this, but came apart just the same. Under these label we can see they used Vision CP 1270 batteries, a different subcontractor from the previous batch.

After the front and back sheets of plastic were removed, both sets of connectors are easily accessible. I swapped out the batteries and reused the wire, connectors, and plastic bracket in between the batteries.

I weighed the batteries just for curiosity's sake. Each 7AH SLA battery weighed 2072 grams, more than double the 940 grams of their LFP counterpart.

I'm sure these terminal connectors are only rated for a limited number of plug-unplug cycles, but here I'm only up to two cycles so I should be OK. If these ever start causing problems, there are vendors selling just the center parts (*) for people who want to build RBC-compatible cartridges from scratch.

After verifying voltage and polarity of the output terminals, I was satisfied this upgraded cartridge is electrically sound and proceeded to mechanical structural integrity. I don't have the big fancy sheets of adhesive-backed plastic, but I do have a roll of clear packing tape that should suffice.

Everything seemed fine when I plugged it in. These batteries shipped only partially charged so I left the UPS plugged in for 24 hours to give it plenty of time to charge up to full. Or actually, the lead-acid standby voltage of 13.8V, which is less than full for these LFP batteries. But "less than full" was exactly what I wanted in the hope of prolonging their useful life. Despite this caveat I expect I'll still get plenty of battery runtime out of this setup, an expectation that needs to be tested.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.