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Description: This is an extremely tiny and light weight battery based on the new Polymer Lithium Ion chemistry. This is the highest energy density currently in production. Each cells outputs a nominal 3.7V at 40mAh. This may sound like not so much power, but the cell is really tiny… like, about half an inch square!

Comes terminated with a standard 2-pin JST-PH connector - 2mm spacing between pins. These batteries require special charging. Do not attempt to charge these with anything but a specialized Lithium Polymer charger. Battery includes built-in protection against over voltage, over current, and minimum voltage. Please use caution when using this battery in wearable projects. When using conductive thread, a short in the thread can create sparks and heat. We recommend using coin cell batteries for beginners.

Note: Due to the requirements of shipping these batteries, orders may take longer to process and therefore do not qualify for same-day shipping. Sorry for any inconvenience this may cause.

Note: Be careful with the JST connectors. They can stick in pretty good and tugging on them can damage the connector. Check this tutorial for an easy way to remove them safely.

Dimensions: 12 x 16 x 5mm

Weight: 2g


  • Excellent long-term self-discharge rates (<8% per month)
  • Robust power source under extreme conditions (-25 to 60C)


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Customer Comments

  • You guys have the shiniest quarters.

  • Dawwwwww, it’s so cute!

  • I presume the maximum charge rate is the usual 1C. If so then why include your existing charging boards in the staff selected links? The lowest current any of them can be set without modification is 100 mA, that’s 2.5C for this battery. The LiPo Charger Basic is even worse, it has a fixed rate of 500 mA or 8C… I would not recommend holding, wearing, or even being within a couple inches of even a tiny a LiPo battery while trying to charge it at 8C!

    • So none of the chargers sparkfun carries would work for this tiny cell because it’d charge it too quickly?

      • Unless the protection circuitry on the battery actually limits the current to around 40 mA or less, yes. After looking at the protection circuitry datasheet, I’m a little more confident that it will prevent an overcurrent from stressing the LiPo (and stressed LiPos can react violently). However, because the schematic appears to be incomplete, I’m unclear if it just totally blocks an excessive current or reduces the current to a safe level. So it’s still very possible the linked chargers won’t work, but it’s also unlikely they’ll damage the battery.

        • With various amounts of annoyance, you can replace the charge rate resistor on our battery chargers to one supporting this battery. The MCP73831T can go down to 15mA, which is within the 1C (40mA) max charge rate. For 15mA, the resistor value would be about 67K. For 40mA, the value would be 25K.

          • Perhaps it might be worth making it a bit easier to change that resistor value on the chargers in future revisions - for instance provide two footprints for that resistor, populate one of them, and make it easy to cut the trace leading to that one if you need to use the other one.

          • how would one go about changing the resistor? The only thing putting off my purchase of the battery and charger is how im going to change the programming resistor..

            do you need to replace it with a surface mount resistor or can you use one with leads.

            • On the board you would replace resistor R3 with a 25K resistor. It is an 0402 surface mount resistor which means the pads are going to be really close together. I think it may be challenging to try to solder the leads of a through hole resistor to those pads. It would be great if Sparkfun would throw in a 25K 0402 resistor with the battery. They are only a few cents each but to order one would cost a few bucks in shipping.

            • +1 I’m also unclear how you’d add a resistor to the basic charger to step the current down to 15mA.

          • Thanks for the reply Mike! However, I still think there should have been some sort of note along these line in the product description.

  • A lot of folks really would like to know the weight of items like this. People using such small cells usually do so because of weight problems. So… you ought to get a scale - probably $30 on eBay. But I’m surprised you didn’t weigh it on your existing scale - just put 10 or 20 or whatever on the scale until you get a useful reading and divide by the number of cells…

    • Weight has been posted! 2g

    • Agreed. Given that I will be strapping this to a 2 liter bottle rocket with a very small board, I would love to know the weight. If its under a gram that would be useful. But otherwise it would be nice if you could run to walmart and pick up a scale.

      • 2 liter bottle rocket? Do you mean a 2 liter model rocket? Because a 2 liter bottle rocket would be very cool… and scary.

    • This will also cut measurement uncertainty by 10 to 20 times :)

  • Any idea when these will be back on stock? I can’t find an alternative anywhere!

  • What is the maximum dissipation current?

  • Hello, is there a datasheet available ? I would like to know the internal resistance and the maximum discharge current. Thanks !

  • If you want really light weight, and don’t mind disposable batteries, you get about the same energy from a #10 zinc-air battery that weighs 0.3g (100mAH at 1.4v).

  • is this.pdf) the datasheet ??

  • It goes to 0 Volt and I cannot charge it. Is it dead? or the protection kicked in?

  • For anyone who doesn’t feel like replacing the charge rate resistor an existing charger, I’ve built a few 40mA USB chargers specifically for these batteries:

  • It would be great if you guys would send a 25K 0402 resistor with these batteries so that we can modify the sparkfun charger to charge these at 1C. Curious, will charging these at over 2C (100 mA) significantly shorten the life of these batteries (or even blow them up)?

  • Can I just slap a variable resistor on the part “PRT-10161” and dial it down to 15-40 mA for the tiny 40mAh and dial it up for the bigger batteries? And of course there would be a readout for the resistor. But would this be possible, or am I just talking out of my ass?

    • Sure, you just need to take care to set the resistor correctly before charging a battery. I prefer to just have two, one set up (and labeled) for large batteries, the other for small.

      Of course it’s twice as expensive, but we’re on Sparkfun. Finding something here that only costs you twice as much is a relative bargain compared to their usual way of business.

  • Can ‘we’ get a clear answer/link? What can be used to re-charge these Li-Po batteries??

    Specifically these 40mA Li-Po’s.. (and the 110mA ones too),… I read talk of chips…changing this or that..

    Is there a product sold that can re-charge these?
    If not…. should probably be noted..

    If the only way is to buy an existing product (ie: and then altering it somehow,..then that also should be noted, with a clear diagram/outline/tutorial on exactly needs to be done..

    Just a simple product that ‘works’… to re-charge these and the 100mA ones)


  • dumb question, what happens if you pull more than 40 ma at a time.. i would assume mah is just the longevity 40ma @ 1 hour but there has to be a limit on current draw right? is that in the datasheet?

  • Just for a bit of clarity, this is a single cell battery outputting 3.7V correct? From the description of “Each cells outputs a nomial 3.7V at 40mAh” leaves the question of how many cells this has open, although the size kind of says it all.

  • It looks like the datasheet is for the 1000 mAh battery.

    • The protection circuit for the 1000mAh datasheet should be the same in the 40mAh.

      • Maybe, but the maximum charging current listed is 2.5 Amps.

        I’m pretty shocked that you don’t take more care to clear that up for your customers. Whether it’s dangerous or not (and assumptions like the ones in this comment thread are how people get hurt) don’t just throw out datasheets without even bothering to specify what they are for.

  • Please post the weight of this product in grams. It is the primary attraction for purchase, but there are no factual details.

  • You could power a single LED for only 2 hours!!!!

  • that’s SO SMALL!!

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