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I have a Sony VGP-BPS21A battery that I use to power my laptop. It is really old, like 5-6 years now and its cells have lost more than 50% of their capacity. As a new OEM is very expensive, hard to find and probably not recently manufactured, I decided to keep my battery controller and replace its 18650 cells.

So everything went fairly well, except I have broken the temperature sensor (a thermistor). Anyway, I have succeeded in fixing it and now my laptop powers on. However, it refuses to charge the battery.

I have checked some parameters my OS retrieves from the battery, and apparently it shows a capacity of 0.0Wh (previously 52.4Wh). I suspect important data was erased from the controller when I disconnected the old cells. I have googled some solutions to reprogram the controller, but only commercial solutions were found. Is there an easy solution to get the controller to charge the battery cells?

I have attached photos of the controller PCB.

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IC1 is the MCU (R2J240 reference).

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    \$\begingroup\$ Once the voltage is removed from the circuit, from what I understand, the code purposely goes into shutdown mode to prevent possible battery explosions from a person recharging a too flat battery. I've never been able to figure out how to reset/reprogram the controller. The best way I can think of is to find another broken controller still attached to a weak battery and keep it powered by an external power supply while you're doing the battery swap. This issue has frustrated me to no end the few times I've tried what you're doing. \$\endgroup\$ – horta Jul 10 '15 at 2:54
  • \$\begingroup\$ @horta Thanks for your comment. I think that's exactly the problem. As far as I have searched, there are ways to reprogram the eeprom, but it requires proprietary software and a probe. Unfortunately, they are way too expensive for me (new battery is cheaper). That's why I ask if it is the only existent solution. \$\endgroup\$ – gstorto Jul 10 '15 at 2:59
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I have tried the suggestion given by Dwayne Reid here to try to recharge the battery with an external power supply, but it did not work, unfortunately.
Apparently, there are only commercial solutions to reprogram the EEPROM of the uC.
I would strongly advise against replacing the cells of your laptop battery, even if you can maintain the uC running. To have a satisfactory result from the replacement, you would need to reset the cycle counter and update the battery characteristics in the EEPROM. That is complicated and expensive to do.

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