k thx for the info I didn't know that batteries dont like to "rest" at full (I always thought the opposite)
a few more questions then ^^
1) wouldn't a simple solution be for the line-in UPS to stop the charging when the battery's at 80% or something? the effective capacity & autonomy would be lower in case of power outage but the battery would last longer
2) for the online this means the battery's being charged & discharged at the same time? I didn't know that was possible for a battery (so this means online UPS batteries are special & can't be used in a line-in UPS or vice-versa?)
3) what about brown-outs don't line-in UPS protect the PC better then offline UPS against brown-outs?
4) also battery output ain't it (usually) better quality in line-in UPS? at least higher end ones (high end line-in UPS => true sine wave but any offline UPS only spits out stepped sine wave which iirc can be dangerous for some PSU's)
and finally...5) if a UPS is of the online type does it by definition automatically imply that it outputs sinewave? or can there be such a thing as an online UPS with only stepped sine wave (eg. iif the manufacturer wanna save costs)