I have the already mentioned UPS. It came to me with a dead battery, so I arranged for a large 12 volt gel-cell battery (brand new!) to be hooked up to it. The UPS charges this battery, but there is something funny going on.
If a "real" power outage occurs, this UPS will simply turn off. It will not go to battery power like it should. For all intents and purposes it appears to be dead. It is certainly not overloaded...all I have attached is one 60 watt light bulb and an SMC 16 port 100Mbit network switch. More often than not the light bulb is turned off, though this does not seem to matter.
But if I "fake" a power outage by doing any of pulling the plug, turning off the circuit breaker or even pulling the house main out, the UPS switches to battery and works like it ought to until the battery is depleted.
I'm pretty sure the large battery is not a problem here. I have another of the same UPS that still has the proper battery in it. This battery works no better in the troublesome unit during a "real" power outage. Likewise, the large battery works fine on the properly functioning unit during a real power outage.
Any thoughts? I'm stumped and I would appreciate any insights on this.