Our new (to us, it's an 1985) P-19 came with an older 86 AH gel battery. I
got a 3-stage StatPower smart charger set to "gel" and charged it up
overnight. Right after charging, the analog volt-meter read 13 volts.
Then I connected a bow light (7.5 watts) to the battery overnight for 16
hours. At the end of the 16 hours, the voltmeter said the battery was putting
out 11 volts. It's an analog meter, so my readings of the gauge lack
precision.
If amps = watts/volts, amphours used = 7.5w/12v * 16 hrs= 10 AH. (please
check my physics on this -did I use the right formula and should I use 12
volts or the 13 volts shown on the meter.). For an 86 AH battery, that's 11.6%
discharged.
The charger manual says that the approximate time to recharge is given by the
following formula:
HOURS = [(Battery capacity in ampere-hours) * (depth of discharge in
percent]/900
According to this formula, the batter should have recharged in about 1.1 hour.
(86*11.6)/900 = 1.1 hours.
However, it took somewhere between 4 and 6 hours for the battery charger to
recharge the battery -- which makes me suspicious of the condition of the
battery. After charging the second time, the voltmeter read 13 volts again.
Can I make any conclusions about the state of the battery from this info? If
the battery is good, would a 7.5 watt bulb use up 11.6% of the amphours of the
86 amphours over a 16 hour period?
Is this battery any good for running lights and a VHF radio? How many
amphours can I expect it to deliver?
Thanks,
Judy Blumhorst
1985 West Sight Potter 19 "Redwing"