Hi all,

I have a very old (but working) 1200VA APC UPS which requires two new
12V lead-acid batteries in series. I want to try and install a different
type of battery chemistry that would yield a much longer service life
than the ~3 years generally specified for sealed lead-acid UPS batteries.

The performance/specs I need from the batteries is as follows:
* 24V
* At least 10Ah
* 20A continuous current output, 50A peak
* As long a service life as possible. 10+ years is good. 20+ years even
  better. 50+ years is perfect. Most important factor. This UPS is built
  like a rock and is already 20 or 30 years old. I intend for it to last
  another 50 years.
* Low cost, but I'm willing to spend more for a longer service life
  battery.
* Indoor use, so flooded lead-acid is to be avoided.
* Regular battery maintenance like water top-ups is not an issue.
* Battery weight and size is not an issue.

I don't expect the UPS to cycle the batteries frequently, or very long.
Power outages can be expected once or twice a month. In any case, all
computers on the UPS will shut down within two minutes of receiving the
signal from the UPS, so the depth of discharge of the batteries will not
be very much.

I will override the charging circuitry in the UPS with a charger of my
own design based on the battery chemistry I use.

I'm thinking about LiFePO4 because I've heard it will last 10+ years. It
also seems to have very good power density.

NiFe batteries would be perfect for this application if I could find a
place to buy them in smaller than 100Ah sizes. Everyone seems to be
selling very high capacity cells for off-the-grid applications.

Any suggestions or tips would be appreciated!

--=20
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