Thanks, both of you! I just found out I may have jumped the gun. I pulled the new battery out of the M3 (which hurt to do!) and put it in my wifes car to move it after her car failed to idle right this morning, died, and wouldn't restart.
The new battery fired the car up immediately into a healthy fast idle, so we'll see how she goes.
1998 328i "M-tech"
2001 TDI Golf. 1300km/tank commuter. Boring, slow, cheap.
1991 P-car: 964c4 Let the porcupine jokes commence.
Gone: '99 M3 vert, '98 M3 sedan, '91 E30, '89 E30, '87 E30, '91 Euro M5, '93 6-speed Corvette, STI v8 swapped '98 Impreza, '73 2002, 2004 325iT