Find solidjake's vid of cluster test...voltage is #9...you can see voltage of car off and on...and you should still do this...or if you have multimeter, just use that and report voltage you have.
If you have new bat, but alt is bad, you'll run into this issue again.
But, hope you just needed battery...although, it could have just been how you were using your battery too...too many short trips, not enough long ones.
I'm so depressed. No one wants to come see me in NYC: Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Mangofy your E46!