Um, I didn't make myself clear, I guess - I took the old one out,
clipped to the new one, instant heat. Big heat.
I'm guessing that there's circuitry which avoids draining the
(bad) low voltage one past a certain point. I'm also guessing
that a fully charged battery (the one I tried to hook up) enables
current flow, and that perhaps the input of the invertor section
is shorted. I didn't feel like leaving a perfectly good 17A-hour
battery to fry itself and the surrounding wires etc.....

BUt thanks for the response / mark


Joseph Gwinn wrote:

In article , Mark
wrote:


I have a back-UPS 400 with a useless gelcell. However, touching
terminals of a fully charged and healthy gelcell to the battery
leads causes mega amps to flow, so something is likely fried.
Interestingly, the dead battery has about 10.5 volts on it,
in-circuit, no current!


This is the classic symptom of a 12-volt lead-acid battery with one cell
shorted. Hooking a 12-volt battery to a 10-volt battery will draw lots
of current, as observed. Replace the old gelcell battery with the new
one; do not keep the old gelcell in the circuit.

Joe Gwinn