You need to measure the battery voltage when it has been on charge for
enough time that you expect it will be fully charged. You said you were
using a float charger. If that's the case, then the voltage on float should
be about 13.8 to 13.9 volts - - the manufacturer has a table for correct
float voltage based on temperature. If the float charger is designed for gel
cells, then its output float voltage will be set somewhat lower than the
voltage AGM sealed lead acid battery requires for float. However, the
battery you have is most likely an AGM, not a gel-cell.

After the battery has been removed from charge for more than 30 minutes,
check the voltage again. With no load and room temperature, a fully charged
battery will have a voltage of about 12.8 volts. A half discharged battery
will be about 12.5 volts at no load.

In any case, you will never fully charge a sealed lead acid battery with a
voltage regulated charger designed to float charge the battery. The most you
can expect is about 80 to 85%. To fully charge the battery, you would need
to bring the voltage up to near 15 volts, but it cannot be left at this
voltage for a prolonged period as the battery will be overcharged and
eventually, damaged. Sealed batteries don't handle overcharging well.

A good automatic battery charger will account for this and switch over to a
lower maintenance charge after the battery is fully charged. If the battery
will not have a load on it while charging, the best charger is a 3 stage
that provides bulk, absorption, and float or maintenance.

all the best,

bumper




wrote in message
ups.com...
All,
I purchased an 8 Amp-hour battery for use in my ASW-20 about 6 months
ago. I had been running a radio, ELT, 302/303 combination, and IPAQ
3800. With that combination my battery would last longer than I wanted
to be in the air; generally more than 5 hours.
I recently removed the 303 and added an SN10B with one meter, so the
electric instrumentation suite is now a radio, ELT, SN10 with one
meter, 302 and IPAQ 3800. At first I didn't notice any difference in
battery performance, but lately it seems the battery has been lasting
progressively shorter periods, and this past weekend the SN10 gave me a
low battery warning after only 2 hours in the air, and that was without
arming the ELT. I keep my battery on the charger on float whenever I'm
not flying, which means it stays on the charger all the time except on
weekends, and it's not even a year old.
Does anyone have a sense of whether I am facing a battery that is
failing, a short somewhere, or simply too many instruments on 1
battery? The battery is a PowerSonic 1280, and the charger is a
standard RR14650A gell cell automatic charger. I also don't have the
tech sheets on all the instruments to add up the current drain so I
can't calculate the expected performance from the battery.
Respectfully,