One thing to note is that with those new optima spiral cell batteries, you don't want to charge them with a charger at all. this is what I have been told by my optima dealer.
The recommend you jump the battery with another for a few seconds. once the car is started, the battery will recharge on its won back to normal power levels.
IF your alternator is faulty, definately check the brushes and replace them. I can tell you that it sucks to get stranded at night with a broken alternator. its happened to me in every car I have owned. once I was a block away from my house. Even a jump start and attempt to drive was useless. the fuel pump would shut off if there was not enough power.
I have no had my alternator stup functioning on my benz yet. My father just had an alternator rebuilt and made more powerful. It cost him over $400 but it went from a a lowly 65 amp to a massive 170 amp. His optima battery will be back to full charge after about 20 minutes with that alternator on it.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.