Rechargeable Batteries, not for everything.

Over the past couple of years I have been using more rechargeable batteries for various things, clocks, radios, kitchen scales etc and generally they work fine. However in a couple of cases the freshly charged batteries have a short life before the device switches off or flashes up low battery warning, days rather than the expected months.
I had a room thermostat that took 2AA cells and last year they needed changing, so stuck in two rechargeable one, all fine then a few days later flagged up low battery, recharged and the same happened. Used two different rechargeable cells and same again days instead of a couple of years. Then put in two standard AA cells and it has been fine since. This last weekend I've had something similar with a digital thermometer.
So what's going on: the low battery warning is often flagged by the circuit measuring the battery voltage and when this hits a certain value it triggers the warning. Non rechargeable and rechargeable cells use different chemical systems where the voltage is slightly different about 1.5V non rechargeable and about 1.25V rechargeable this means the warning triggers a lot sooner for rechargeable cells; although the cells are still almost fully charged.

 

I have come across the fact that certain items only work well with non rechargables.
Never actually understood why though.

 

The makers of my twin macro flash setup recommend non-rechargeables if using in burst mode.

 

I never put them in clocks, they go flat in a few days whereas 'proper' batteries last much longer (although not as long as they used to)

 

With rechargeable batteries I always make sure that I buy a good make i.e. Duracell. Also ensure you buy the ones with the highest power rating in milli amp hours mAh. Currently this is 2500 mAh for the AA size , and 900 mAh for the AAA. A good charger is recommended, one that tells you when the cell is fully charged, as this can take up too 8 hours. In clocks they will last up to 6 months. I do find that the TV remote control eats the AAA batteries. I don't have any high demand items, so find the rechargeable work fine for me.