Is a CMOS battery rechargeable?

Is a CMOS battery rechargeable? If so, what does its charger look like?

Timo Huovinen

Posted 2011-03-01T13:09:08.773

Reputation: 551

Answers

Most CMOS batteries are CR2032 lithium button cell batteries and are not rechargeable.

There are rechargeable batteries (e.g. ML2032 - rechargeable) that are the same size, but they can't be charged by your computer.

Andy

Posted 2011-03-01T13:09:08.773

Reputation: 740

4We're assuming that Yuri is talking about a desktop. Many Laptops have a small rechargeable battery to backup CMOS. – Chris – 2011-03-01T13:46:18.400

2so the CR2032 are NOT rechargeable? why don't I ever see them run out in a desktop? – Timo Huovinen – 2011-03-01T14:17:12.690

2@Yuri: The CMOS battery is only used when the system isn't connected to any other power source. So most of the time they're not being discharged at all, and a battery designed for such use can handle sitting on a shelf for several years without losing much of its charge. Until you unplug your PC and find that your BIOS settings have been reset, you probably won't know that the battery has died. – afrazier – 2011-03-01T14:31:18.260

3@YuriKolovsky - They do run out, I've seen it a lot. Generally it takes at least a minimum of 5-7 years though. – Shinrai – 2011-03-01T15:38:54.647

@YuriKolovsky Mine died :) I had to replace it. They tend to run about 10 years or so, depending on use. Since most replace desktops every 3 or 4 years or so, you may never see it die. Even if they do die, you just have BIOS CMOS settings go to default, so you may not notice it. – Rich Homolka – 2011-03-01T15:40:14.493

Will the battery holder on most boards automatically charge an ML2032? (For some batteries, having power applied to their terminals is enough to charge them. Is it the same with the ML2032? Does the port have power applied to it when it's not draining, or does it go into high impedance, or what? -- Suppose, it's probably different for every board, and I'll have to break out the voltage tester.) – BrainSlugs83 – 2014-03-17T18:40:18.960

Found this rechargeable BIOS battery hack -- don't do it if you're afraid of voiding warranties or breaking out the soldering iron -- also, I'm pretty sure the choice of Ni-Cad is important (as Li-On would probably last longer, but has a more complicated charger circuit). Will post back if I see any further developments. :-)

– BrainSlugs83 – 2014-03-17T18:51:29.810

Some motherboards used to have rechargable CMOS batteries on them.

In general now, no CMOS battery (especially the silver button cell type) are rechargable without investing in a specific rechargable version.

Do not - I repeat - DO NOT attempt to recharge a non-rechargable lithium cell (button type) as the resultant explosion and noxious gasses could kill you (or worse).

Majenko

Posted 2011-03-01T13:09:08.773

Reputation: 29 007

4A CMOS battery has insufficient power to kill you or even hurt you seriously.There is insufficient reactive element in it to do much damage. 18650-like cells are a different matter. Those can start a fire quite easy. – Overmind – 2017-01-26T08:10:01.827

1Kill or injure, no, but a button cell could produce a decent thermal reaction that could potentially damage internal components or the motherboard. – JW0914 – 2019-12-10T04:59:13.523

It could definitely injure you. There is more than enough energy to create a small, but very intense fire, more than capable to give isolated 3rd degree burns and act as an ignition source.

Fumes would be rather limited due to the small amount of electrolyte, so they likely wouldn't be a concern unless there was a lack of ventilation. However, such a fire could ignite other materials. – Robert Wm Ruedisueli – 2019-12-10T07:12:44.753

A standard CMOS battery is not rechargable.

It is a CR20XX type cell, typically a CR2032.

The battery lasts 5-10 years depending on the particular board it is put in. This means it lasts longer than most rechargeable cells would last even being recharged. There is no reason for it to be rechargeable.

Robert Wm Ruedisueli

Posted 2011-03-01T13:09:08.773

Reputation: 167