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My digital calipers take a 3V 2032 (coin cell) battery, they currently contain a CR2032 (lithium manganese dioxide). It's on the very low end of remaining charge, I have no spares, and no easy way to get any today.

I also have a variable DC power supply, although I can't use it to directly supply the calipers because I need to use them far from the AC power outlet. The supply allows me to set the voltage and limit the current at the same time.

Given that I don't care about this battery, and I just need to stretch it a little longer (i.e. this is a one time thing then the battery gets disposed of -- and if it ends its life in a small ball of fire and lithium fumes, I'm OK with that), if I just hold 3-4V across it for a while, can I give it a little bit of charge back?

If so, what's a reasonable voltage to apply to it (and current limit) and what's a decent metric of when to stop? Will I need to do it in intervals to manage heat or anything?

Or have I been living a lie my entire life and LiMnO2 batteries are actually supposed to be rechargeable?

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    \$\begingroup\$ Tip: "if I just run 3-4V through it for a while ...". You apply voltage across a device. The current runs through it. I don't know if you can recharge CR2032s but if you can you will have to limit both the voltage and current to a safe value. \$\endgroup\$
    – Transistor
    Commented Sep 18, 2021 at 15:23
  • \$\begingroup\$ @Transistor This supply lets me set the voltage and also limit the current, so that's a plus. I don't know what the safe values are, though. Thanks, though that's a good starting direction. \$\endgroup\$
    – Jason C
    Commented Sep 18, 2021 at 15:25
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    \$\begingroup\$ If you've got a PC that you don't mind resetting the BIOS on, you could use the CR2032 battery from it temporarily. \$\endgroup\$
    – Andrew Morton
    Commented Sep 18, 2021 at 15:26
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    \$\begingroup\$ Digital kitchen or bathroom scales are a handy source too. :^) \$\endgroup\$
    – Transistor
    Commented Sep 18, 2021 at 15:27
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    \$\begingroup\$ Wear PPE, there's a good chance it will go bang at some point \$\endgroup\$
    – NMF
    Commented Sep 18, 2021 at 15:38

1 Answer 1

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Panasonic CR2032 specification says:

Nominal Voltage (V)             3
Nominal Capacity (mAh)          225
Continuous Standard Drain (mA)  0.2

I would try it with a 4 V source limited to 1 mA. A 4 V supply with a 1 kΩ series resistor should be safe.

I suspect that if the battery is flat that it may not recover. It might be enough to get you by though.

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  • \$\begingroup\$ All right. Those are numbers. I didn't have any before and now I do. Works for me. Will let you know how it's looking shortly. \$\endgroup\$
    – Jason C
    Commented Sep 18, 2021 at 15:48
  • \$\begingroup\$ Yes, monitor the voltage across the cell as a matter of interest. If the internal resistance has gone very high you'll see close to 4 V on the cell. I've written a little about cell internal resistance here. \$\endgroup\$
    – Transistor
    Commented Sep 18, 2021 at 15:57
  • \$\begingroup\$ So this has been running for a while now; I think it's working but it needs a lot of finesse. Something I noticed is that if the supply voltage across the cell ever exceeds 3-ish (not sure exact value), then the cell voltage (with supply disconnected) begins to decrease. But if I keep the supply around 2.95 or so, the cell voltage begins to increase again. It's slow, though. It started around 2.51 and now it's up to 2.78, which is promising. Experiment continues. Target is 2.95 I guess. \$\endgroup\$
    – Jason C
    Commented Sep 18, 2021 at 18:12
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    \$\begingroup\$ If you'd told us you were prepared to do chemistry I'm sure you'd have got suggestions on using lemons, coins, vinegar and all sorts of other stuff. Well done. \$\endgroup\$
    – Transistor
    Commented Sep 18, 2021 at 18:16
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    \$\begingroup\$ Thanks for letting us know. 15 to 20 V was definitely excessive. I would have been afraid to go above 5 V with current limit. You may have blasted some ions back to where you need them. \$\endgroup\$
    – Transistor
    Commented Sep 18, 2021 at 20:00

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