I found this puzzling....

Body

Did you know a solar panel & controller that charges battery at 14.5v at 10amps takes 145 watts output from PV panel. Alternative about twice that power must come from any non-solar source for appearance of equivalent 145 watts charging power to that battery. Why? Short answer is non-solar power must apply twice the voltage to overcome battery back-voltage. Measure your a/c powered battery charger input W into battery compared to line power cost. Compare a 100watt RATED solar panel battery current and voltage power into same battery. 100 w of solar current did what it took 200 w line source to do, same work/effect! Amazing considering 98% eff new SST battery chargers. 
50% of the power is wasted in a line powered charge circuit folks! But every availible DC watt typed on PV ratings sticker converts gets used by the battery. 

When your FE box ain't chooching..
During no or weak PV harvest don't use a generator or utility to only charge batteries, use it on all other loads and/or to help bring charge current to available solar/other charge current minimizing charge time, cost and noise. Shake flooded cells often release bubbles, keep acid SG even. Trojan T-105RE new carbon/graphene lead tech. so far so good.
Botton line I measure more than the rated PV power being used by the battery, go figure that in your hardware lab, what say u?