Rechargble batteries, why do they seem to have an aversion to smoke detectors?

Rechargeable batteries, why do they seem to have an aversion to smoke detectors?

I have ten smoke detectors fitted, each "stand-alone" i.e. not connected to the mains or each other.

Thinking I'd save money and the environment, I bought a rechargeable battery every time one of the ordinary non-rechargeable batteries ran down as replacements.

All went well until the rechargeable ones started to run down, causing alarms to beep as a low battery warning, this after about 9 months in the detector.

I recharged the batteries according to the instructions and measured 9.5 volts across the terminals. Replaced the batteries, within 48 to 72 hours off they went again. I can still measure the 9.5 across them.

This has now happened 3 times, the rechargeable batteries, if tried in different appliances, work fine.

At wits end, any clever people out there with any ideas??