Smallest rechargable battery?

Hello, I would like to use the MDBT42 with a battery and a recharger, which is as small as possible. What is the smallest size for such a battery? Maybe the same like in Smartwatches or smartrings. I don't need a really large battery lifetime.

Sun 2019.12.22

MDBT42Q module 1.7v - 3.6v or MDBT42Q breakout board 2.5 - 16v?

The breakout board.

Sun 2019.12.22

What will the load be? LED's, temp sensor, GPS? Will impact the best choice.

Google is a fantastic resource to discover answers like these. . . .

Range of watch batteries using Google: 'rechargeable watch battery' see image at page bottom

http://www.w4zt.com/batteries/

A typical standard for power consumption and delivery is the CR2032

https://data.energizer.com/pdfs/cr2032.p­df

A fully charged Li-Ion CR2032 may damage a MDBT42Q module however

https://www.powerstream.com/p/Lir2032.pd­f

Datasheet for the smallest CR1220

https://store.comet.bg/download-file.php­?id=14803

For the breakout board where voltage is a bit more forgiving, consider a micro copter drone battery. Will need a separate charging board for constant current charging.

Abount the same size as the breakout board 852540 Lipo

https://ebay.to/2MzMOBh

It appears the drone battery route has already been discovered a while back

http://forum.espruino.com/conversations/­337020/

If you want something really small with battery and charger, I'd recommend just buying a mini USB power bank.

You can get ones that go on a keychain, and they have a charger and small battery inside. You can just open them up and connect the breakout (which will easily take LiPo voltage - it'll go up to 16v or so) direct to the battery terminals.

Sorry for bringing up an old topic, but it kinda fits:

I'm using a (fresh) CR2032 battery on my Pixl.
When I switch on the backlight it flickers when ever code is executed, i.e. clock updating etc.
It also flickers when typing in the WebIDE console.

Is this normal behaviour for running Pixl with a CR2032 or do I happen to have some minor quality batteries that can't provide the necessary power/voltage under load?

I'm afraid it happens on all of them - the extra power draw just drops the voltage enough to dim the backlight. At 3v it's not much above the voltage needed for the LED so any dip in voltage is very apparent.

A decently big capacitor on the 3.3v line would help but at the end of the day if the calculation goes on for more than a small fraction of a second you'll still see some dimming.

To be honest using the backlight on CR2032 won't be amazing - it's not as bright and the increased power draw will flatten the battery a lot more quickly than might happen otherwise.

For a bit of a late follow-up here, I've been looking for similar, and have been using the Panasonic ML-920S/DN - it's an 11Mah 9mm x 2mm coin cell that can be recharged by feeding it 3V. I'm still in the midst of testing it, but for my purposes (a day of intermittently clicking buttons on the MDBT42) it so-far seems to work OK, though I'm still messing around with TX power to avoid big peak draw.

You can see it on the bottom of the board in the attached photo.

1 Attachment

That looks really interesting - thanks for posting it up! I guess even just adding a big (47uF?) surface mount capacitor might help enough to get rid of any issues with power draw from advertising?

Thank you Gordon! Adding a capacitor appears to have prevented a bunch of dropouts :)