To charge a lead acid battery regardless if
if it is liquid, like your car battery, or has a
gelled electrolyt, requires a higher voltage then
the nominal rated voltage be applied.

Broadly speaking there afre three classes of lead
acid service.
Starting, cycle, and flaot.
The first is your typical engine atarting service.
Requires gobs of vurrent for short periods and loafs after that.
Cycle is like for golf carts, fork lifts, VHS camcorders, and in truth
the way I used to use a gell cell to power my SW for weekend
radio picnics.
Standby is for "emergency" loss of power applicaitns like emergency
lightst in public areas, PC UPS and the like.
And each service has different suggested charging voltages.
See:
http://www.osibatteries.com/pdf/Gel%...ies%202004.pdf
for one take on the correct charging voltages.

Cars charge batteries at up to 15V. A gell cell wll get hot and fail
very rapidly at that voltage. I have found 13.69V to be good voltage.
Some go as low as 13.5 or so. Much below that 13.5 and the battery
will not charge.

Half these for 6 volt batteries. I have a couple of 6V gell cells
designed
to power camcorders that I use with our DX398 for week end radio
picnics. One DX398 will operate for over a day on a single battery.
To get slighlty longer run time I could charge them at ~7V, but I prfer
for my batteries to live longer then run longer.

Everything is a trade off. Longer run time for fewer charge/discharge
cycles.

At home I would just operate everything from my 12 gell cells, I have
linear step down regulators to reduce the 12V to 9V and 6V as needed.
With each devcie protected by a OVP after the reduction regulator.

If I knew a power outage was going to last a "long time", I would power

our DX398s from the 6V gell cells. I scalvaged 4 PV (solar cells) from
some dead lawn night lights that produce ~150mA at 4V in bright
sunlight,
by making 2 parallel sets of 2 in series I get 8V at ~300mA. With a
simple shunt regulator I get 6.845V,more then enough to keep the gell
cell topped off and operate 2 DX398s at the same time.

I have a couple of older Arco ~12V PV arrays that produce 18V @.75A
in bright sunshine, so I could recharge my 12V gell cells and or
operate some equipment during daylight hours. Remnants from the cold
war when the great nuke out seamed likely.

Terry