When the air conditioner in the trailer kicks on it often triggers the UPS's to kick on. We had all the computer systems and disk drives on the smaller unit, the APC SmartUPS 1000. Perhaps on hot afternoons, when the ISS trailer air conditioner is also running, the power surges are larger.
In any case the SmartUPS 1000 was shutting down on every AC turn on, since it eventually drained its battery after so many hits. This causes disk problems, which is NOT good. We now have the USP's cabled in serial, with the SmartUPS 1000 plugged into line power, the big SmartUPS 22XXX (whose battery is toast) is plugged into the 1000, and the computer systems are running on the 22XXX. It seems to work better than with the 22XXX first in line.
We've asked Kurt to order a new battery for the 1000.