rechargeable headphones (batteries and charging questions)

[Cadmaster375]

I just scored a deal on a set of 900 mHz sony headphones ($2.00). They come with a rechargeable battery pack and charge stand) the NIMH battery pack can be replaced by drycells (non-rechargeable) AAA batteries if the Rechargeable battery dies or is out of charge. They designed the headphones with a little button switch in the battery compartment that lets the charger know that it has the Sony rechargeable battery pack in and to charge the battery when on the stand. I tested the battery pack and one of the AAA sized cells reads 1.3 v and the other cell reads 0 volts (dead cell). the replacement Sony battery pack is about $40 locally and the rating on the Sony NiMH battery pack is 2.4 v 550 mAh. My thought is that I can replace the dead Sony Battery pack with 2 NiMH 1.2 V 850 mAh AAA cells (4 rechargeable Duracell AAA NiMH batteries cost $20) and use the charging stand to keep the Batteries charged. Rather than removing them and using a standard battery charger to recharge them. My belief is that Sony made the battery pack nonstandard so they could make more profit by selling the replacement rechargeable batteries. All I have to do to get the charger to work is insert a small piece of electrical tape into the battery compartment to depress the little button switch.

Can anybody see any problems with my thoughts? as far as I can see the only problem is the headphones will past longer on the new batteries than the old battery pack. Since both battery pack and individual batteries are both NiMH charging them on the charging stand should not cause any problems as far as I can see.

My plan right is to modify the 900 Mhz transmitter and use it and the headphones on my metal detector if possible or buy a small 900 mHz transmitter and mount it to the detector