On Wed, 21 May 2008 17:23:06 -0400, Meat Plow wrote:

I bought a couple APC Back-UPS XP 1000's in 2004. One is on my A/V
equip in my living room and one in my office. I also have a Back-UPS ES
350 on my DSL modem, wireless router and Linksys NSU1 network storage unit
bought around the same time. I've never had any problems with those units.
The 1000's self test on their own at regular intervals and the 350 still
runs for 45 minutes with the equivalent load of a PC with two hard drives
minus a monitor. Trust me I've had my fair share of failed APC units but I
have yet to figure out why some last for a year or so and others seem to
last forever. If I had to guess I would say it's the quality of the
batteries if the unit just sits there not being called upon for backup and
suffers an untimely death.

IME the difference is more to do with the battery (re-)charging and maintenance
charging regime. Too often the manufacturer's arrangement is designed for
maximum recovery rate (minimum recovery time) after a discharge, and they also
tend to float them at a high terminal voltage. Almost without exception, every
failed UPS I have checked had cooked SLA/VRLA batteries. That cooking came
about at the hands of the charger, not the internal temperature of the unit.

soapbox It is similar to the fate of Lithium-Ion laptop batteries. The
appliance manufacturer's objective is maximised operating time, so they charge
to 4v2. Charging to 4v1 would give something under 20% less usable capacity,
but double the cycle life. The manufacturer would rather quote 3 hours
endurance than 2.5 hours, so he configures the machine for maximised sales spec.
The user picks up the tab later. /soapbox