Where to buy (thin) lipo batteries?

[CookieEater]

Hello!

I'm hoping this is the right section to ask this sort of question. I haven't seen anything that is dedicated to sourcing parts.

For a project I am looking for very small lipo batteries. <3mm thickness, ideally around 2mm. Obviously they can be thinner. Capacity about 70mAh, bigger is better.
In terms of the other dimensions, one can be about 4cm (that is below 1 2/3 inches), and the other as small as possible as well, I would be fine with 3cm (1,2 inches).

I'm not sure yet about the peak current usage as I am still in the planning stages. I would assume not more than 100mA, some of it I can surely buffer with a capacitor as the main load will be a PWM signal with 50% duty cycle.

I know these are very specific dimensions, especially the thickness constraints, I'd love to explain.
I'm designing a wearable placed inside of a semi-flexible casing. It needs to be as small as possible, and I'm planning on using the circuit board as an outer shell surrounding the battery, giving it some mechanical protection (apart from other measures), hence my requirement (among other reasons) for the battery to be quite thin.

I'm not sure where to get batteries like these. I'm having issues finding sellers shipping to Germany at a reasonable price, moreover they're obviously batteries so getting them from a reputable source and of decent quality is important.
I also thought about going about this a different way and trying to find replacement batteries for a pre-existing product (i.e. smartwatches and other wearables) which happen to fit my requirement, but no luck so far as they often don't come with dimensions in the product descriptions, or they are unfortunately too expensive or too thick.

Maybe one of you can point me in the right direction. Thank you!

[Karmaslap]

Not quite to your spec, but a 68mAh 3.3mm battery here:
https://www.renata.com/en/products/lithium-polymer-batteries/icp281029hpg/

You could fit about 4 of these in the volume you described. I'm not sure that 3.3mm would work but I'm not sure where to find thinner off the top of my head either. You might be able to use a hybrid rigid/flex board and some foil for the necessary protection and save on thickness.

[CookieEater]

Thank you!
I also just stumbled upon rechargeable coin cell batteries? I didn't know they were a thing. Obviously they would also have the advantage of being in a very very hard casing.
I found some 2032 rechargeables, which barely cut the discharge current and capacity specs. They seem to come in the coin cell battery typical solderable packaging as well with the spot-welded leads on there. I could go up to a 3032 and that would be just perfect but I'm not finding these.

You might be able to use a hybrid rigid/flex board and some foil for the necessary protection and save on thickness.

I meant like my pcb would have a hole in the middle for the battery to be put in, and not on top of the pcb. A thinner pcb wouldn't help me there, or maybe I misunderstood.
Sort of like this:

[Smokey]

Check these guys out.  Lots of stock battery sizes.  They were surprisingly easy to deal with.

https://www.dtpbattery.com/

[Karmaslap]

https://li-polymer-battery.com/ultra-thin-li-polymer-battery/?gad=1&gclid=EAIaIQobChMI0v-C_PqRgAMVfg6tBh2XtAJvEAAYASAAEgI_EvD_BwE

thinnest batteries I could find, actually just googled "ultra-thin lithium polymer battery" and it was at the top. Pretty crazy how thin these are.

[liaifat85]

You can check its measurement
https://polybattery.com/product/3-7-v-80mah-ultra-low-cost-lp541415-small-lipo-battery

[tszaboo]

Thank you!
I also just stumbled upon rechargeable coin cell batteries? I didn't know they were a thing. Obviously they would also have the advantage of being in a very very hard casing.
I found some 2032 rechargeables, which barely cut the discharge current and capacity specs. They seem to come in the coin cell battery typical solderable packaging as well with the spot-welded leads on there. I could go up to a 3032 and that would be just perfect but I'm not finding these.

You might be able to use a hybrid rigid/flex board and some foil for the necessary protection and save on thickness.

I meant like my pcb would have a hole in the middle for the battery to be put in, and not on top of the pcb. A thinner pcb wouldn't help me there, or maybe I misunderstood.
Sort of like this:

For coin cells, their designation is "LIR". So a LIR3032 would be the search term you are looking for. If the battery doesn't fit your application, maybe build a battery pack with more than one cells.
I would suggest to safety test it because it's a wearable.

[CookieEater]

Yes, and those are pretty hard to find.
Generally speaking, I am aware of the sites posted in #4 and #5, but I don't know how reputable they are, and moreover I don't need 100+ batteries. I'm mostly building the device on my own for now and while I would love to commercialize it, I don't see this as a feasible option for many reasons. Realistically, I don't see myself purchasing more than 5 of these.
Apart from LIR-type cells, I did notice there doesn't seem to be a naming scheme companies necessarily adhere to, or there seems to be some (mis)use of these as a format factor/replacement they could function as, or a lot of batteries I found through parametric searches are actually mislabeled as rechargeable.
Regardless, I also found a possible candidate in lithium nickel manganese cobalt oxide based cells which look very promising, even though their price tag seems to be pretty hefty (10USD+). The candidates I'm talking about here, as an example, are RJD2032C1ST1, RJD3032ST1 and RJD2430C1ST1. Unfortunately apart from the price I also haven't found a distributor or shop shipping these to Germany, yet.

[I wanted a rude username]

The first constraint you hit with mainstream (cheap) Li-ion prismatics is generally not the thickness of the cell, but the thickness of the protection circuit. This is usually ~3.5 mm because due to using a thick PCB and having the cell's terminals wrapped around it. You can solve this by putting the protection circuitry on your PCB and ordering cells without it (with either flat terminals or wires straight to the cell). Then you can certainly find 3 mm thick cells, and probably less but 3.0 mm is the thinnest I've ever ordered.

[CookieEater]

Oh, interesting!
So, for example, these are neither reputable (I assume), nor do they meet the thickness requirement of 2,7mm stated in the description?
https://www.aliexpress.com/item/33006447669.html

[radiolistener]

For a project I am looking for very small lipo batteries. <3mm thickness, ideally around 2mm. Obviously they can be thinner. Capacity about 70mAh, bigger is better.
In terms of the other dimensions, one can be about 4cm (that is below 1 2/3 inches), and the other as small as possible as well, I would be fine with 3cm (1,2 inches).

something like this?

https://www.aliexpress.com/item/1005005441604831.html

https://www.aliexpress.com/item/1005005517388160.html

https://www.aliexpress.com/item/1005005743100200.html

https://www.aliexpress.com/item/1005005441690799.html

[CookieEater]

More or less, yes.
Again, how reputable is this seller in this case?
I have zero issues ordering from ali, and from shops with even 96% positive ratings, but I only order harmless and non-critical components like buttons, switches, LEDs, sockets, ports, etc.

[I wanted a rude username]

You can ask the seller to measure the thickness with callipers. Send a photo showing the kind of measurement you want. 2.7 mm is feasible, and if you're only risking USD $20 for 10 units it seems worth it. Sellers don't usually want to screw you, because they like repeat business. The bigger issue may actually be the shipping time, because a lot of sellers will only ship cells by surface mail.