Not necessarily. If you're sitting at idle with the rear window defroster on and the seat warmers going, I'd expect your voltage to be under the low charging limit. As long as the voltage comes up to 13+ at 1200-1500 RPM, you're probably fine.

2002 X5 3.0 316,300 miles
2014 428i 24,800 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - under restoration