Successfully replaced the battery with a third party one

[mifritscher]

My cosmo had a inflated battery as well. I searched for a third batttery which fits into the cosmo (soldering is fine for me), but the biggest problem was the required thinness of the battery (original name: SXX600, original size: 13.6 x 6.2 x 0.3 cm, original capacity: 4220 mAh)

Eventually, I stumbled over https://www.ampul.eu/de/batterie/4452-li-pol-akku-3000mah-37v-306090, which is  9.0 x 6.0 x 0,3 cm and has 3000mAh. The size is almost perfect - 2 dimensions are fitting completely, the other being about 4 cm less. Which is actually rather good, because this way I have some space for the cable. soldering etc.

Both batteries - the old and the new - have a tiny pcb with 2 (dual) mosfets and a tiny controller. On the original pcb, there is not only P+/P- on the connector, but also an ID and a "Test" line (is written on the connector cable). I used both PCBs - the old one for satisfying the id+test lines, the new for a additional safety layer. And because it was the easiest way :-D

My biggest fear was that the pcb locks itself if there is no voltage anymore on the battery cell side as a safety measure (quite common on laptop batteries). To avoid that, you have 2 choices: temporary connect an external power supply ( 4,4V, 100...200 mA will do), or connect the old and new battery in parallel. I went the second way, which is easier, but needs a bit of preparation.

The main problem is to prevent a high current at the moment of connecting the both batteries.

Luckily, my old battery had already a quite big impedance because of its defect. If you have a power supply with adjustable voltage and current (or a current limit of max. about 2A): Measure the voltage of the battery (in my case: 2.9V) Then apply a voltage of 0.1 V (max. 4.4V) more than that. If the current is less than about 1 A (typically: _much_ less, 50 mA is a typical value): Go up to 4.4V (or, if you have already the new battery: 0.1V more than that, should be about 3,7... 4.2V, mine had 3,9V). If the current stays under 1 A the old battery is either full or has an high impedance. Both is good.

If the old battery has an _higher_ voltage: discharge it until the voltage is a bit under the new battery.

The old cell was connected to its PCB via contact welding the connectors. Luckily, soldering right on the connectors works fine. So I soldered first the black wire of the new battery on the old PCB (mind the polarity, there is also a "B-" on the PCB). Then I hold the red wire on the B+ connector on the old PCB. No smoke ( :-D ), so I soldered the red wire on it as well. Then I disconnected the alu connector of the old cell with a scissor (please do not short anyshing :-) ). Then I isolated everything, taped it with duad side tabe and screw everything together again.

Result:
1. Cosmo started, displaying a SoC of 64% and 3.9V
2. It charged fine and linearly up to 100%
3. It discharged fine and linearly up to 0%, lasted the predicted time (about 11 hours with quite a load - hint: disabling the cover connection with the app and the cover in the "quick selection" area helps ;-) )
4. It chaged finde and linearly up to 100% again, with an internal measured (with AIDA64) energy of 2946 mAh - perfect strike :-)

Pictures:
 

 

P.S. This should work on the gemini as well.

[jakfish]

This is great to hear.

Jake

[346L3]

Thanks for the hint with the batteries!

I successfully replaced my bloating battery with this one.

2 things I want to add:

- There is no need to keep the board "live" with  connecting a PSU or auxilliary battery. The Cosmo will fully function after being left without a power supply for more than 48h

- You can desolder the small protective PCB of the replacement battery, clip the battery contacts a bit and directly solder the original PCB to the battery instead of the red and black wires. They have matching contact spacing
A small bit of kapton tape and the replacement looks exactly like the original, albeit a bit shorter.
 

 

[pogmommy]

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.