After roaring and fuming, this power supply gets my vote and the only viable battery charger that will do whatever you want it to.
It is portable. Unplug it and run.
It has adjustable voltage. The ideal 14.8 volts for generator charging and it will MAINTAIN a preset 14.8 volts and YOU not some a nineteen cent integrated circuit decides when to end the charge rate.
Combined with a solid FIFTY AMP continuous output rating it will recharge batteries as fast or faster than so called Smart chargers costing twice as much,
Tell you what, you get this charger and when you unpack it I will walk you through the setup process step by step*. You will need to buy a cheap set of 10-gauge jumper cables as a connect to the battery umbilical.
You can unplug the unit when finished or install an inline cord switch. Or even a windup timer.
Need to equalize batteries? This is the perfect power unit.
*Not an idle promise.
Offered as gifts I would select this power supply 10 to 1 over any smart converter on the market for use as a battery charger - and it costs less.
http://www.trcelectronics.com/View/Mean-Well/RSP-750-15.shtml