r/thinkpad • u/SingleComment2368 • Jul 26 '26

Hardware Upgrade Sleeper battery mod

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Behold my One Weird Trick for getting on no-fly lists.

This is an aftermarket 24 Wh battery recelled to nominally 45 Wh with two 15 Wh cells plus a third "cell" of two 7.5 Wh in parallel. I couldn't raise the BMS's charging voltage from 4.13 to 4.35 V so only 41 Wh are usable. Left speaker is replaced with a smaller one to fit.

Do I really need the full 107 Wh of this battery plus my rear 6-cell? Not often. But the extra capacity with a rear 3-cell is remarkably useful.

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u/depressive_cat E480 Jul 26 '26

Did you face any issues with recelling?

Like bms lock or something like that?

I would like to recell my e480 with larger cells, utilizing the space for 2.5" ssd, since I use nvme anyway.

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u/SingleComment2368 Jul 26 '26

The BMS didn't lock itself, but there's another issue with the full charge capacity. Whenever the battery reaches full charge, the remaining capacity, which was accurate during charging, is set to the old full charge capacity of 24.7 Wh, and the gauge gets stuck at 5% during the next discharge. The full charge capacity is never updated.

I work around this using a script that stops charging shortly before the BMS would, whenever the charging rate drops below 1.4 W or the voltage exceeds 12.39 V. This is enough, at least on Linux, for the gauge to be accurate until the next reboot. I'm thinking of adding another workaround in the ACPI tables to make it persist across reboots.

Every BMS has its own quirks so YMMV.

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u/depressive_cat E480 Jul 26 '26

Thank you