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« Last post by pogmommy on June 29, 2026, 02:00:32 am »
Hi all, apologies for posting to a long-inactive thread. Wanted to share my experience doing a custom battery swap.
Huge thanks to mifritscher and 346L3 for sharing their battery replacement experiences. Thanks to them I was able to bring one of my Cosmos (which had been dead-on-arrival) back to life. I'd purchased it online as seemingly new-old-stock from a third-party, and it arrived with a bloated battery and showed no signs of life, even when plugged in.
I tried using a Huawei Ascend P6 battery after seeing in daffyduck's thread and the linked article- the Cosmo became more responsive with the Huawei Ascend P6 battery, but consistent with jakfish's comment in that thread, it did not seem to actually charge. It would power on though as if it were charging though, which it would not do with the bloated OEM battery, so that gave me hope that a BMS swap to a new cell would get it working again.
I can confirm 346L3's comment that the BMS doesn't lock up if it loses power- my bloated cell seems to have been in such bad state that my multimeter was reading zero volts from it, so i figured if it was going to lock itself, it would already have done so. So I didn't bother keeping it powered during the swap, and cut away the original cell.
After soldering the new cell to the board, it booted fine and read the new battery as being at 35%, which lined up with the ~3.81V I'd measured from it.
I did not remove the BMS of the newly-installed cell, I just connected its positive and negative wires to the corresponding terminals on the BMS (with a JST connector inbetween but that's not important), which seemed to work fine. I also used a higher-capacity cell (6500mAh) than the Cosmo originally shipped with (4220mAh) since I was unable to get my hands on a 3mm cell with comparable capacity for a reasonable price, and plan for this device to be mostly stationary and for development purposes. For reference, I used a 3.7V 956090 (0.95 x 9.0 x 6.0 cm) LiPo cell, which definitely does not fit in the original housing as it's a little over 3X the thickness of the battery mifritscher linked to, but I'll likely be replacing it with something more reasonable later. I may try looking into 3.85V batteries of similar sizes/capacities made for other phones that I can swap the original BMS onto, if they're easier to get for a decent price.
Apologies for the lack of pictures, with this being my test device this initial assembly isn't particularly pretty, nor does it really show anything you can't see in mifritscher or 346L3's pictures. This was my first time doing work like this on batteries, but I do have soldering/small electronics repair experience and I found this incredibly easy to do.
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