PX Battery replacement

[zingo_apc]

I bought a PX40 in 2003, when should I change the batteries? - speaking of which do I need to change them all together or is there some way of changing only those that are failing?

[karbonphiber_apc]

I concur with cmarler - the lifespan of a battery is dependent on the temperature in which it operates in, discharge/recharge cycles, and chemical integrity. The Panasonic 7.2Ah, offered with the Symmetra PX, is a premium non-industrial VRLA battery which should last anywhere between 2-5 years, provided the above mentioned parameters are maintained within the manufacturer's specs.
You never want to mix old batteries with new batteries. As batteries age, their internal resistance increases which will cause the DC charger in a UPS system to decrease it's float voltage. Old and new batteries will not be equally charged which could result in longer charging times after discharge, less efficient and incomplete charging, excessive heat generation, etc...

[zingo_apc · Accepted solution]

I bought a PX40 in 2003, when should I change the batteries? - speaking of which do I need to change them all together or is there some way of changing only those that are failing?