CR2032 batteries

[ElyDave]

Nominal voltage of 3V, what constitutes "dead"

I've just measured a couple that I took out of things in some fault finding mode and they are 2.8V, which I'm assuming is still good.

[spesh]

A brand-new CR2032 straight out of the packaging will usually read 3.3 volts, which is why most devices running off them give a "low battery" indication at 2.8 volts, in my experience.

If you are lucky, you may have a device which can still work down to 2.75V and eke out a bit more, but it's a crap-shoot.

[hellymedic]

The load taken by your meter is less than that taken by your gadget and the voltage will drop under load.

I'll check some fresh spendy 2032s if I can do this without a Packaging Battle.

I think I'd try a fresh battery empirically, though I appreciate  they are spendy and a bit awkward to source.

Teh Kim might be more helpful...

[Canardly]

7 day lithiums are reasonable.

[Kim]

I'd agree that 3.3V is about right for an unloaded brand new cell.  This will drop a bit under load.  If you look at a discharge curve for a LiMnO2 cell, it's pretty flat with a steep drop off towards the end of life (especially at higher currents), and there's not a lot of energy left once it drops below about 2.7-2.8V.

[Diver300]

There is little energy left in a 3 V lithium battery below 2.7 V, so it was somewhat satisfying when I found that the battery from one of our remotes was at about 1.5 V just after it had stopped working. That remote had been quite good at scraping the energy barrel.

Devices differ enormously in their ability to work from batteries that aren't new. Some devices will be spectacularly good, like that remote, and other will stop with a battery that is still more than 3 V. Little LED lamps running on CR2032s or similar are often very poor, in that the light output starts dropping immediately, and while they will run for ages from a battery at 2.8 V, there is next to no light output with the low voltage.

[hellymedic]

[Slightly OT] David had a laser pointer thing that needed new batteries. I put in on CR2016, thinking it ran on just the one. It lit but seemed feeble.
I only realised later I should have used two.

D'oh!

But it did light...

[Kim]

Bike computers are great at running on almost nothing.  You only notice when you go out in the cold the following winter and the display has no contrast.

The use of CR2032s for lighting irks me.  While little LED lights like that make sense as an emergency backup option, it seems like a particularly inconvenient and wasteful power source for routine use.  Yet they seem surprisingly popular amongst the BSOists.

[T42]

I used to have one of those wee frog-like rear-lights mounted on the bars & pointing backwards to illuminate the bottle-cages & transmission. Only for occasional use, though.

[Kim]

I used to have one of those wee frog-like rear-lights mounted on the bars & pointing backwards to illuminate the bottle-cages & transmission. Only for occasional use, though.

Yeah, I have some on my mountain bike as a backup to the obnoxious eBay MTB light, tend to carry a couple of strap-ons on night rides just in case, and a little keyring LED torch thing permanently installed in my tent inner to aid finding my proper torch in the dark.  They're good for that sort of thing.

[ElyDave]

Thanks all, the ones I am questioning are from my Garmin sensors, two at 2.8v, but I think they are ex a standby light.

The one in the Garmin sensor is at 3.0v but the Garmin was refusing to talk to it yesterday for some reason, although blinkylights were saying all OK.