Originally Posted by drabina
The battery is going to power a headphone amplifier.
Thought it might
Then you may want to check the amplifier shuts the power down when the battery is down to 7V or so. Alternatively fit a LED which switches off at 7V. Not as reliable but better than no indication at all.
Most likely if you continue to use the amp until the sound starts to distort, your NiMH battery will be very unhappy indeed. It won't break immediately, but you will seriously reduce the number of times you can recharge it.
Depending on how you use it, buying a load of Alkaline 9V PP3 batteries may turn out cheaper in the long run.
Unfortunately PP3 style 7.2, 8.4 and 9.6 V batteries are a poor configuration for NiMH and NiCd rechargeables as the internal cells are not individually monitored during charging and discharging. They mostly find use as backup batteries on a very
low trickle charge. They are still fairly cheap batteries and I do not know of a supplier which fits polarity reversal protection diodes for each cell in this battery format.