3.7v Li battery (x2 series configuration Teclast T-51 DAP)

[13hm13]

I have a Chinese branded  Teclast T-51 DAP (digital audio player) which is the same as the Nationite s:flo2 model.
Looks like an early iPhone. This model is from 2010.

Inside are TWO batteries apparently in series (balanced) config. I have not taken the protective wrapping off the batts to see the exact wiring config. or the protection PCB. I'm going to assume each battery has its own PCB. I can measure the voltage to about 7.2v when fully charged (which isn't long). The unit  charges via std. micro USB (5.0 v).
Yes, they lasted 12 years in fairly regular (daily)  use for about 10 years.  But now, time to replace the battery!

Dimensions: 25x90x5mm for EACH battery.

I can find NO info on the OEM batt., so no clue as to mAH capacity, etc.

Ali and ebay have several options.
 Please suggest something given the parameters I have provided.

Photo below of interior of DAP with batt:


Photo below of exterior:

[ledtester]

...
Inside are TWO batteries apparently in series (balanced) config...
Dimensions: 25x90x5mm for EACH battery.

I can find NO info on the OEM batt., so no clue as to mAH capacity, etc.

Ali and ebay have several options.
 Please suggest something given the parameters I have provided.

So you have lipo cells in a "2S" configuration. Lipo cells come in all shapes and sizes so it is a matter of finding a supplier for the dimensions you need.

If you search for "2S lipo" you'll get a lot of listings but the two cells are usually stacked on top of each other. One of those could work if the two cells are not glued together and only held together by tape. I'd ask the seller for confirmation of that.

Performing a search on aliexpress for "lipo cell" yields a lot of hits for largely unprotected cells.

I would contact this seller which has a pretty high rating:

https://www.aliexpress.com/store/1101115656

and say you're looking for two lipo cells which will fit in a 5mm x 50mm x 90mm space. This leaves open the possibility of using cells of dimensions 5mm x 50mm x 45mm as well as 5mm x 25mm x 90mm. Of course, you can always use smaller sized batteries.

(You may have noticed that the "model number" of the battery is basically an indication of its dimensions -- e.g. a "755590" battery is 7.5mm x 55mm x 90mm.)

Once you find suitable cells, I would transfer the protection board from the old pair of cells to the new pair. The yellow tape that you see wrapped around the protection board is called "Kapton tape". It's a thin, high-temperature resistant tape and it's a useful to have around when repairing electronics. The green tape holding together your old cells is also probably Kapton tape.
 

[13hm13]

...
Inside are TWO batteries apparently in series (balanced) config...
Dimensions: 25x90x5mm for EACH battery.

I can find NO info on the OEM batt., so no clue as to mAH capacity, etc.

Ali and ebay have several options.
 Please suggest something given the parameters I have provided.

So you have lipo cells in a "2S" configuration. Lipo cells come in all shapes and sizes so it is a matter of finding a supplier for the dimensions you need.

If you search for "2S lipo" you'll get a lot of listings but the two cells are usually stacked on top of each other. One of those could work if the two cells are not glued together and only held together by tape. I'd ask the seller for confirmation of that.

Performing a search on aliexpress for "lipo cell" yields a lot of hits for largely unprotected cells.

I would contact this seller which has a pretty high rating:

https://www.aliexpress.com/store/1101115656

and say you're looking for two lipo cells which will fit in a 5mm x 50mm x 90mm space. This leaves open the possibility of using cells of dimensions 5mm x 50mm x 45mm as well as 5mm x 25mm x 90mm. Of course, you can always use smaller sized batteries.

(You may have noticed that the "model number" of the battery is basically an indication of its dimensions -- e.g. a "755590" battery is 7.5mm x 55mm x 90mm.)

Once you find suitable cells, I would transfer the protection board from the old pair of cells to the new pair. The yellow tape that you see wrapped around the protection board is called "Kapton tape". It's a thin, high-temperature resistant tape and it's a useful to have around when repairing electronics. The green tape holding together your old cells is also probably Kapton tape.

Good, useful info!
That Lanzhd  Ali seller seem ideal. Ali's English search is atrocious. They could sell a lot more stuff out of China/HK if they invested more time in other languages.
Didn't know the sizing code, either. What about that second code next to "+"? Could it be the capacity and voltage?

[ledtester]

What about that second code next to "+"? Could it be the capacity and voltage?

The voltage of a single lipo cell will always be "3.7V".

In this pic:

https://www.aliexpress.us/item/3256802569830553.html

the "20200101" next to the "+" is likely a date code.