A little late maybe, but it might still help.
I had battery charging problems a while ago. It turned out to be the alternator, who had a faulty field diode, the red warning light never went off completely, the battery died slowly. Also the mechanical Bosch regulator had burned in contacts. I had the alternator overhauled by a retired car electrician, and replaced the regulator with an electronic one : CAR GO nr. 130675. It's 1/3 of the height of the Bosch, the installation holes match, and I paid 35 Euro's.
I also have a 77 Ah battery since 5 years now, problem free till now, (1500 km's a year).
Willy, 230 SL 1967 - 220 SEb 1965