A good test would be to measure the voltage of the cells while the Bit is charging. The NiMh cells should show a higher voltage under a heavy load than alkaline batteries. This is why they work so much better in flash cameras, the flash needs a high inrush current to charge the capacitor. This may be the reason why they don't recommend rechargeables for the Bit. The charging current may be too high. The internal resistance of the alkalines may serve as a "regulator' of sorts........