The inverter stays on for 2 seconds no matter what the load. The
batteries are fine, as stated, a new inverter works fine on the same
batteries.

I have a fair amount of experience with electronics, just need some
pointing in the right direction.

R




If you're unsure about the battery, the simplest test is to disconnect it
and measure its voltage. Around 6.3 V (6 V nominal) or 12.6 V (12 V
nominal) is probably pretty good. Down to maybe 6.0 V or 12.0 V might be
salvageable. If it's way lower than these, like less than 4.0 V or 8.0 V,
the battery is junk. If you think the battery might be salvageable, hook
it back up and leave the inverter plugged into the wall but not powering
anything for a day. Then disconnect the battery again and check the
voltage. If it came up significantly, there is hope, but if not, get
some new batteries. You might try measuring the battery voltage while
the inverter is starting; if it drops too low the inverter will shut
itself off. This may be difficult to do in the short time you have;
another test is to take the battery out of the UPS and load it with
something like a car tail light bulb to see what the voltage does. The
on-load voltage will always be a little less than the no-load voltage,
but if you use a typical tail light bulb (about 2 A) and get 12.6 V
no-load and less than about 11.5 V on load, the battery is probably
toast.

Be careful when fooling with inverters; they are designed to make
line/mains voltage at a fair amount of current.

Matt Roberds