12.5 volt 7 amp sla = 87.5 watt hours at 1/10 - 1/20 of the c rate.
2 of my thor batteries has 7 amps at 1/20c printed on them.
c rate = rate of discharge that = dead battery in 1 hour.
with a fresh charge about 85 watts is disapated in the 100 watt bulb.
small battery - no alternator...