>How many amp hours in a typical alkaline C cell?
>This locomotive draws 400mA at full PWM.  Wonder how long it will run?
4500 mAh @ 10 mA continuous, 3200 mAh @ 100 mA continuous, so perhaps a
bit less at your 400 mA draw. Sounds like 4 hours or so...

Source: The Art of Electronics, p. 923

Dave Johnson