-> In my ignorance here, I have an old Sears Craftsman 6A automotive type
-> charger, 6V/12V, and I've used it a number of times in testing/charging
-> gel cels. From memory, when I connected to the commonly-used 12V 7AH
-> batteries which would take a charge, it would typically start out
-> showing about 3A on the meter, then taper down pretty quickly to 1A or
-> so. AT those charge rates, battery would typically get warm, but not hot
-> enough to split the case, or any other disasters.  I've heard of gel
-> cels 'blowing up" when being charged too rapidly.

That is codrrect, they can blow up. But only rarely. And if you feel
Heat dusing charging you are Most likely Overcharging them .HEAT is the
Wrost Enemy of a Gell Cell. They dry out very easily and you cannot
replace the Lequid. 
Once again USE a Specialized Gell CEll charger as a First choice, or as
a distant second best a charger rated at NO more then 1.5 amps for those
11 Ah batteries.


-> FWIW, and IME, 'bad' gel cell batteries I've seen would generally not
-> even start to accept a charge - the bad ones I've seen seem to have
-> failed to an "open" condition.

That is theri Most common Failure Mode. It is caused either by
Overcharging Abuse or Letting them sit too long and they Totaly
Discharge. For Gel Cell batteries not in use or on a special Maintaining
Charge charger it is recommended they be charged every 3 Months to 4
months..

-> So I think Mark is pretty much safe if he sets his charger to the 2A
-> rate.

I Don't. Those battery chargers have Very poor voltage regulation(Which
determines Amp output) being designed for Large Ah batteries with Liguid
Electrolyte that can take some overcharging. 

->  MM> Put a 12V automotive bulb on them that draws about two Amps, like a
->  MM> dome light bulb.  A tail light will run about three Amps, a stop light
->  MM> about 5 Amps, and a headlamp about 8 Amps.

As I mentioned in another post a #1156 is an easily availble Automobile
bulb and will do the job. Calculate the discharge time using 2.1 Amps


-> OK but I think the battery capacity isn't that linear - - probably
-> tapering down during more rapid discahrge rates.

That Ah rating does go down for Heavy Discharge rates. For the Very
paqrticualrly you should discharge the battery at the anticipated load.
that is the meaning figure that would be most meaningful for a Computer
System.


-> The APC 420 Smart UPS Pro unit I have here just uses a 12V 7AH battery -
-> - just 84 watt-hours of power. Figure in my system unit and this 17"
-> monitor, and if those suck up 240W or so of power, I figure I'm down in
-> the 15-minute range of reliable backup power, with this battery now a
-> couple years old. Looks to me like this type of UPS unit is clearly
-> designed just to give a user time to shut things down just after the
-> power goes off, not to provide multi-hour protection and continued
-> operation.

BINGO, give that man a Cigar. Those mickey mouse UPS units aqre ONLY
designed to give a orderly shutdown of the system they are protecting. 

And as stated elsewhewre rembe,mber those units are alos NOT Full Time
Duty machines .So adding batteries to increace the backup time will
mostly end i ndisaster if you try to extend the time too much.
They do make 24/7 capabile units but as I have said before IF you have
to ask the Price you Cannot afford it.
You can shave a bit off the prices of ready built units by Checking some
of the Solar Power Sites. They have a full range of 12 VDC to 120 VAC
inverters, heavy duty batteries and Suitable battery chargers.
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