I use my Mega Watt for boost charging only. The old Sears 6/2 Amp manual charger at 16.0v gets the nod for EQ charging after the Mega Watt is done. 2 or 3 hours on the Sears usually gets the SG as high as it's going to go on a Single T-1275. I can tell it's usually finished when the amp meter starts at 6 amps or a bit more, and drops to 50% of the rating, or 3 amp charge rate, on the analog meter.
Are you running good 8 gauge wire or thicker, with premium connectors on the ends, with a short run from Mega Watt to batteries? You can lose voltage there also.