Battery time

Last weekend I tried driving the M3 and got nothing but faint dash lights. First I thought I left something on, but most everything in the car is automatic and I'd been in and out of the garage lots the two weeks prior. I found a decent multimeter at Action Auto Parts. They didn't want to sell it to me at first (Strange concept, stop a customer from buying). I convinced them I would find many uses for a multimeter and they finally let me buy it ($14). My friend Kevin and I were amazed at an astounding low voltage from the battery. We jumped the car and got it started, after realizing that we didn't have to put jumper cables into the trunk (BMW puts batteries in trunk, not up front). I then realized that the brief time running the engine wasn't going to charge the battery enough to trust it. I picked up a 3 amp maintainer and hooked that up. Over the following 3 days of charging I tried starting the car and almost got it to turn over once. The whole while checking the voltage and seeing numbers all over the place, typically low. I finally conceded defeat and picked up a battery from www.batteriesplus.com "Werker BCI Group 94R Luxury and Import Car Battery - SLI94R-LI‏". That cost me about $160 after taxes. The alternative was $220 at Capitol Hill BMW and about the same at Bellevue BMW. After the 30 min drive to Everett and the 1hour drive back in rush hour traffic I'm not sure saving the 80 bucks was worth the painful commute.
I'm going to install the battery tomorrow after work. That should do it.