Not all rechargeables are alike. I would not recommend NiCads. They have too many problems, like memory. I would recommend Nickel Metal Hydride types. Each detector pulls a different rate of amps so life span varies.

NiMH batteries:

I use exclusively the 9 volt Varta 150 mAh. I got these for about $1 on ebay new. They work great and NiMH have no memory problems. You do not have to run them all the way down like Nicads. They do test at 9 volts fully charged. NiMH come in slow and fast charge types. Match the charger to the type or else. NiMH chargers are not like NiCad chargers. They typically have a timer to shut them off. These "9 volt" batteries come in a range of voltages and are listed as 8.4 volt, 9 volt, 9.4 volt and even 9.6 volt. Like Nicads they are internally composed of 1.2 volt cells. So they really ought to be 8.4 v or 9.6 v. Some folks rant and rave about 9.6 volt being such a deal because they start out higher. I don't think this is such a big deal. Most electronic devices have internal voltage regulators and step down or restrict the maximum voltage anyway. I bet the Fisher CS does too. If we knew the precise cut off the CS voltage regulator uses then I would agree the voltage might make more of a difference. The real difference in duration is the mAh (milliamp hour) rating. Watts=Volts X Amps. It's all about Watts folks. Based on a well charged and properly burnt in battery, my 150 mAh ones run 5 to 13 hours on the CS using the speaker. If you use the light expect more like 5. I simply carry the spares in my pocket or switch them over at lunch when I have the time. I spent $4 for all the batteries I will need for the next 10+ years! NiMH batteries go up as high as 260 mAh. The greater the mAh the more the cost. Fast charge often costs more than slow charge too. Everyready & RayOvac make slow chargers that do 2 batteries for under $20. Chargers also come in car models or combo models. Remember you need a 2 battery charger. To see a listing of the very hottest 9 volt batteries on the planet click here. I'd imagine you could find these same batteries cheaper somewhere, but this is the best comparison I know of. They sell the matching chargers too. The iPower 260 mAh are the current champs.

Note: Make sure you burn them in charging and discharging them fully five times. If you get 2 sets of batteries then rotate the ones you start out with each time. Always do a fresh charge the day before use.

hh

-=john=-