C385 Alternator/Voltage Regulator

I recently became the owner of C85#71 and took my first extended cruise on her last month. I discovered that the two 4D batteries she came with aren’t enough to keep up with the load when I run both the refrigerator and the freezer (which seem to pull an average of about 5 amps, or about 120 amp hours in a day, too much for the 160 amp hour rated battery.) I don’t have a genset, so the only way to recharge the house bank when not plugged into shore power is to run the engine. But at the rate the original alternator charges up, it takes at least a couple of hours to top off the house bank.

I understand that part of the problem is that the internal regulator on the alternator isn’t designed to do a rapid recharge of a house bank. I’m considering installing an external voltage regulator, and maybe replacing the alternator. The alternator that came with the boat is rated at 125 amps, bigger than the 55 amp version I gather was standard on some of the earlier hulls. The current alternator should be plenty big, but I don’t know if it would be possible simply to put on a Balmar or other external regulator, rewiring the alternator to take the internal regulator out of the circuit. Or would it be better to replace the alternator, too? I’d appreciate any advice.