On Wed, 10 Oct 2012 09:06:59 -0700, Jeff Liebermann
wrote:

I've found that the quality and survivability of gel cells can be
estimated by their weight. Light weight batteries don't have enough
lead and will die an early death. The differences are fairly subtle
for small 50A-hr gel cells, but become obvious with the bigger
batteries.
http://groups.google.com/group/sci.electronics.repair/msg/d2e2cb9eb130b695

I don't know what constitutes a SMPS (UPS) rated gel cell.

In a particular size/case manufacturers often list a couple of types,
aimed at general duty and UPS-type duty. The latter are reputedly
optimised for the higher discharge rate found in that role compared to
the more urbane alarm system backup role (which only hits decent
discharge current if an audible alarm device is exercised).

The batteries I buy claim that the battery can be used in everything
from electric toy cars to USP's with little distinction as to type of
service.

Claims and reality are often strangers.

What I've found is that many UPS's over charge their
batteries.

Indeed. IMOE the things that kill UPS batteries a

1. excessive float voltage
2. the heat that results from 1
3. far too aggressive recharge after discharge

A bit off-(thread)-topic, but I have a $20k+ communicatios test set
that uses Gates cylindrical sealed lead-acid cells in the battery
pack. The inbuilt charger design was such that these sets seem to
kill packs ina couple of years. Tiring of this recurrent cost, I
rejigged the charging circuit some 12 years ago, and haven't had a
pack die since. Sample of one isn't generally considered
statistically significant, but this is to me.

Measure the charge current at various discharge levels and
I suspect you'll find that many UPS's are trying to squeeze the last
bit of power out of their batteries in order to give longer runtime.

Just as laptops do ...

They also tend to recharge rather quickly, in order to deal with
repetitive power failures.

Yes, almost universally.

I had a running battle with APC over this issue on some of their
products. Note the pile of rack mounted (forgot the model number) APC
UPS's piled up on my deck:
http://802.11junk.com/jeffl/pics/home/slides/BL-house3.html
There were many many more that were ummm... recycled because the
batteries got hot, bulged, and eventually leaked electrolyte all over
the equipment. This UPS used four 12V 7A gel cells in a 24V
series/parallel combination.

I have been called on to "service" quite a number of failed soho UPS'
of varying sizes from 150W to 4kW, mostly APC. The electronics are
almost universally fine - except for one with dead FETs in the
inverter, the failure mode in every single one was batteries. When I
bothered to check the charge regime, it was found to implement the
above rules 1 and 3 on how to kill UPS batteries.