TW> All of them I know about use sealed Lead Acid Batteries.
TW> They are "Float" type Batteries and they do not tolerate deep
TW> discharges very well so if you run them all the way down too many times
TW> they need to be replaced.

True.  I have an extra UPS that I'm not using at the moment, but I leave it
plugged in and charged all the time.  

If you leave them off for long periods of time, they will end up not
working anymore.  We have had "spare" UPS batteries sitting in
our computer room at work sometimes for up to 2 years.  When you go to use
them, they almost never work after sitting that long with no charge.

- Mark

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