On Thu, 8 Jan 2009 16:49:34 -0800 (PST), mkaras
wrote:

mkaras wrote:
I have several Belkin Model F6C120-UNV UPS units in need of repair.

Thanks folks for the replies. I disassembled one of the UPS units (a
unit in service since 2004 or so that failed about 4 months ago).
Inside it looks clean except the batteries are completely dead. If
particular interest is bulging of the sides of the battery cases.

A sure sign of overcharging, electrolyte drying, and heat damage.

I'll
try getting two of units of these 12V/7.5AH sealed batteries (appears
like a bog standard type of battery) and see how that works.

If you don't attend to the charging circuitry you'll get the same outcome.

The comment from Van Chocstraw illustrates the problem:

"I put 2 motorcycle batteries in series and put
them beside the UPS. Drilled a hole in the UPS and ran a wire to the
battery terminals. Works like a charm though it DOES tend to Overcharge
the batteries. They bubble all the time and dry out. Have to keep adding
water."

The manufacturers aim to recharge the batteries in the absolute minimum time
(often with the absolute least-component-count chargers) with the argument that
the next AC supply outage could be very soon. The casualty of this thinking and
poor charger design is battery life expectancy.

Hell, I have a piece of communications test equipment that was ~$US18K new. The
battery charger in these was sub-standard and all owners I know have to replace
the batteries every two or three years. I reworked the charge system many years
ago and haven't had a problem since.

I want to watch battery cost even though these things were about $180
US when new. A quick look seems that locally at Batteries Plus the
replacements are about $33 US each for the "Werker" brand. Mouser web
site shows an equivalent Panasonic unit at $39 US each but then there
is shipping on top that.