How many amp hours is your battery bank?
Why will it not fully charge from whatever you started at to 80% full in just 4 hours?
Will unplugging the charger re-set the 4 hour timer? If you take away the 120 volts for say 10 minutes, and put enough load on the battery to get it below say 12.4 volts?
Why not just install a few solar panels, and let that system keep the battery full all the time?
You can buy a 140 watt solar panel for about $229 with aluminum frame. If you wanted to wire a bunch of them in series, then a MPPT controller will give you the higher than average voltage you are looking for. Or a PWM controller is very low cost, and will leave more of the budget for buying panels.
SunElec.comBy the way, a MPPT controller should be able to switch 12 volt power up to say 14.5 volt power, but I have not tried it. I did consider it as a way to charge a trailer battery from the long line leaving the truck alternator, but find that solar panels are much less expensive. But I have also heard that a MPPT controller will short circuit the panel output while charging it's internal capacitors, so not sure if it might work, or short out the system?
14.25 volts should be enough to fully charge a battery in a reasonable time, without overheating the battery. I found that my golf cart batteries got warm when charged at 45 amps with my Trace M1215 inverter/charger in my RV, it has a 70 amp charger max rate, but I normally adjust it to only 50% charge rate to both keep the fan off, and keep the battery voltage from getting so high that the battery might warm up. Personally I do not like the charge voltage over 14.0 volts.
Good luck,
Fred.
