I have started using NiMH to power my many battery-powered clocks around our house.
I'm using the Amazon labeled, 2000mAh, pre-charged type AA cells.
My first test of a wall mechanical clock with a powered pendulum went for slightly over 9 months.
Not likely as long as an alkaline AA but that's still okay for me, since It saves a little money, and I don't have to trash a dozen batteries every year.

 

Are those similar to the eneloop batteries?

I have used the eneloops successfully in low average consumption devices, to avoid the potential chemical leakage of alkaline cells. The eneloops have a very low self discharge rate.

 

I'm getting ready to replace the batteries in all of the smoke detectors (have ten of them) and think I might get twenty NiMH batteries. I keep batteries in a fridge, so I the plan would be to swap out the batteries, charge the ones I just took out, then put them in the fridge and use them for the next swap six months later.

 

Are those similar to the eneloop batteries?

Similar, in that they have a low self-discharge rate (about 10%/yr), but I don't know how they compare otherwise.

 

How does it help keeping battery in the fridge? Does that reduce the self discharge?

Lastly, what temperature are we talking about? 40F or whereabouts?

 

How does it help keeping battery in the fridge? Does that reduce the self discharge?

Yes, in theory at least.
I keep all my batteries (alkaline and lithium) in the fridge (40°F or so) to reduce the self discharge.
The speed of most chemical reactions are reduced by 1/2 for every 10°C drop in temperature, due to the reduction in molecular speed and energy.
You could keep them in the freezer for even more reduction, but then there's the concern about the long-term effects of below freezing temperatures on the batteries.

 

Yes, in theory at least.
I keep all my batteries (alkaline and lithium) in the fridge (40°F or so) to reduce the self discharge.
The speed of most chemical reactions are reduced by 1/2 for every 10°C drop in temperature, due to the reduction in molecular speed and energy.
You could keep them in the freezer for even more reduction, but then there's the concern about the long-term effects of below freezing temperatures on the batteries.

I have been using NIMI for my clocks for at least ten years. I recharge them every daylight savings change. I don't remember losing any of them. They are mostly from Batteries Plus store so there is nothing special about them.

 

I tried using enloop in a 1 AA type wall clock with hands and it sometimes stopped. After investigating I found out that the clock required about 1.4V for reliable operation, though it would usually run at less. I "fixed" it by changing it to use 2 AA NiMh in
series regulated to 1.4 volts (didn't want to overvoltage it, 2*NiMH even though nominally 2.4V can worst case be almost 3 volts).

 

I found out that the clock required about 1.4V for reliable operation,

That seems unusually high.
Most of my clocks seem to run down to near 1V before stopping.

 

It would run down below 1.2V but sometimes stop. And wouldn't start. At 1.4V it's sure to start and run until the NiMh batteries are really truely drained. It's an old clock I picked up many years ago at a swap meet. The clock says "Junghang Technology" on the face. Inside is the usual cheap 1AA movement with plastic gears, however the plastic is thicker than some more recent made in China movement I tried. Power averages about 140uA which is one 2.5mA pulse every second for 45mS.

 

How does it help keeping battery in the fridge? Does that reduce the self discharge?

Lastly, what temperature are we talking about? 40F or whereabouts?

It reduces self-discharge in some battery types (zinc-carbon and lithium) and doesn't accelerate it in any (that I know of). I think the impact on alkalines is minimal and I don't know about NiCd or NiMH. So it's mostly a matter of hedging your bets. There's concern about condensation when stored at refrigerated temperatures, but I live in a pretty arid climate and the fridge I use has an exposed freezer compartment that freezes out the moisture in the air making the compartment very dry -- I used to keep a container of desiccant in there, but even after a year it showed almost no sign of collecting any moisture. As for temperature, it is whatever it is. I'm not convinced that there's enough of a difference to make it worth the effort of doing anything more than closing the door. Plus, it's a 50+ year old dorm fridge -- it's not going to regulate the temperature very well. I just stuck a thermometer in there and let it sit for about ten minutes and it is showing dead on 40°F.

TBH, a big part of the reason that I use it is because I have it, have nothing better to do with it, and it makes it easy for me to keep track of where batteries are when I need them and a place for me to put batteries when I buy them. Without it, they would end up scattered around the house (like everything else).

 

I think the impact on alkalines is minimal

Why do you think alkalines would be different from other battery types?

 

Why do you think alkalines would be different from other battery types?

It's not that that I think, out of the blue, that they would be different. But neither do I just assume that all battery chemistries are going to behave the same in this (or just about any) regard.

From what I have read over the years from battery manufacturers and other sources I found reputable, the bulk of the arguments seem to take the position that alkalines don't exhibit any useful extension in shelf life by being stored at lowered temperatures. But there are plenty of differing opinions and a ton of noise out there on the subject, so I don't have a definitive answer.

 

the bulk of the arguments seem to take the position that alkalines don't exhibit any useful extension in shelf life by being stored at lowered temperatures.

Perhaps that's because the alkalines have such a low self-discharge at room temperature, that reducing that is not significant for practical storage times, not that lower temperatures don't reduce it.

 

Perhaps that's because the alkalines have such a low self-discharge at room temperature, that reducing that is not significant for practical storage times, not that lower temperatures don't reduce it.

I don't know. I also don't know whether refrigerating them has a different impact today given the pretty obvious change that has been made to most alkalines such that they now have significantly shorter shelf lives and a much greater tendency to leak. Probably not, but who knows.