It actually depends on the which battery (mfr and model) are used. But if you take their (or anyone's) so called "standard" offering, plan to replace them every 4-5 years. On paper they might say about 7 yr life expectancy. Do not count on it.
The above opinion is not a reflection on the make or models of UPSs you mentioned. Just a general observation on small VRLA batteries.
Even the 'premium' VRLA types with a claimed 10-year life will start having their first casualties after four of five years. Most of the cells will be still be good, but you only need one bad cell in the string and the battery is crippled. VRLAs don't tend to show a gradual failure: they are more often there one moment and gone the next. As Rafiq said above, that's a general observation about VRLAs - I don't know which VRLA brands Liebert and APC are using these days.
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If we learn from our mistakes I'm getting a great education!
ScottyUK makes a valid point, one bad cell or battery in a string makes all of them useless. I have used various brands of VRLA batteries from 6 to 180AH in telecommmunications applications over the last 20 years. I eventually adopted a 3 year replacement cycle for all batteries large or small, because avoiding one outage and the associated overtime call out nearly makes up the added cost in my case.
Granted for a 40kw UPS your battery cost is considerable, but the whole point of a UPS is reliability. I would not plan on more than 4 years before battery replacement in any case.
Flooded cells: the old ways are still the best. Higher capital cost and arguably more maintenance (although the latest recombination cells are claiming 15 - 20 years between top-ups) - but nothing touches them for long life and reliability.
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If we learn from our mistakes I'm getting a great education!
I try to do quarterly internal impedance checks if there's not a battery monitoring system. Even with that, you can still get caught with an occasional surprise failure. Lower cost VRLA should be replaced every 3-4 years at most. Some of the better grades can go a bit longer.
Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.
