Voltages are read with the charger in operation. Because of the larger size bank of the OP his power supply is striking a "more reasonable" intensity of charge because of the large bank capacity. If power supply operation slows way down at say 14.7 volts, let's give it a 3.0 charge rate for fun - then that's too slow. The power supply should do better than that. Offering a "feel" for how many amperes are flowing at different levels of voltage here is vital. Otherwise advice is being given while being blindfolded. Not worth spit.
AMPS WHILE TOP CHARGING. HOW MANY AMPS? This means the Megawatt is running...
At
13.50 volts?
13.75 volts?
14.00 volts?
14.25 volts?
14.50 volts?
14.75 volts?
14.85 volts?
14.95 volts?
15.00 volts?
How LONG in minutes did it take to go from start to 15.00 volts? Can the Mega stay charging at 15.00 volts and maintain an inflow of more than 10 amperes? Or does the amperage drop like a stone?
Note: This is where a "smart charger" would need a good dose of thorazine. It simply does not have the computing power to figure 1% of the above information, out, never mind deal with it...