And, you'll discover on one UPS the UPS won't turn on because it doesn't
see a battery; on another, it won't run it's self checks; etc. You don't
know what "firmware A" expects of it's battery that "firmware B" doesn't.
All of the battery-backed products I've designed predated lithium. Put
a lithium battery in them and they'll throw a fault -- because the
battery isn't discharging at the expected rate; or is charging at
the wrong rate (dv/dt); or, the monitoring circuitry appears defective; etc.
"Hey, let's make this lithium battery look EXACTLY like a lead acid -- so
it HAS NO ADVANTAGES over a lead acid battery! But, we can charge more
for those non-differences!"
MSRP $1,865.88 <https://www.amazon.com/dp/B08QQRFQ4W
MSRP $2,899.99 <https://www.amazon.com/dp/B09JR6ZCQX
$1000 premium for lithium battery pack. Same exact run-times,
same load capacity, same networking capability, same display
(literally the same module). Ah, but the more expensive one has
a shiny front panel (and isn't intended to be floor-standing)!
[Latter has shallower aspect ratio and weighs less -- though at the cost
of an additional rack unit. *Might* be important in a datacenter;
doubtful a SOHO user would bother with it as he'd likely not have
many such devices, many batteries to replace, etc. Note the number
of lead-acid offerings vs. lithium -- why is that?]