Donald I have a shop here in LA that muscles up alternators to high amp current flow.
As I mentioned somewhere before. Had my dad's alternator in his rolls rebuilt from 80 amps to 170 amps. It now charges like there is no tomorrow.
The only problemw ith these kinds of rebuilds is that they charge best once the engine is spinning faster than idle, but the thing charges very nicely. with everything turned on in the car, it barely even puts a load on the car now.
Good luck on your quest for the new alternator. Have they checked the regulator?
My father had similar issues with his rolls after the alternator rebuild, and it turned out to be a faulty battery. After we had it changed, the car has not had a problem.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.