They only last for a 4-5 months before the detector starts chirping to say the battery needs recharging. With five detectors I'm recharging one battery or another frequently and it has become a bit of a PITA (but it's still worthwhile given the high cost of non-rechargeable 9 volters).
Is this frequency because they are only 8.4v or is it down to the mAh? Googling just now I see that you can get 9.6v rechargeables which the suppliers claim you can use in just about anything that needs 9v i.e. in gear where 8.4v can't be used. I also see you can get rechargeables with, say, 500 mAh.
Would appreciate thoughts.