Does anybody have a recommendation to a source of consistently good replacement batteries for the X230? The last (/first) time I tried buying an aftermarket battery, the thing lasted perhaps 6-12 months and then turned into trash. I've got it in my head to do some DIY cell swaps some day, but it's so far down on the list I'd settle for an off the shelf answer if I knew I could avoid fraud.

The big disadvantage of the T420s/430s is the s batteries do not use standard cells. The T420/430, X220/230 (and I assume w series) battery packs use standard 18650 cells.

In the x220 battery packs the controllers are not locked down hard (the later x230 batteries appear locked down and cannot be reset the same way... likely need either special software or may be able to connect directly to flash). The controller (bq8030 or bq2090 or similar) nvram can be dumped and written using the laptops built-in battery management smbus.

I recently re-celled mine; dump the calibration nvram before starting (not the end of the world if you didn't). Buy whatever power tool battery is on clearance. Swap the 18650 li-ion cells. For a cheap and cheerful spot welder, you can buy a board with some FETs to switch power from a car battery. Restore the firmware. Run Lenovo battery calibration.

Lots of info at http://www.karosium.com/2016/08/hacking-bq8030-with-sanyo-fi... (no affiliation, but found it a great resource!). If you didn't save your firmware or starting from a toasted battery, compare and contrast to calibration dumps found online. TI also has general specs available on a similar controller.

The battery controller will set a bit to disable the battery when the cell voltages get out of sync when removing/adding cells (other ways of dealing with this too.... holding controller in reset, voltage in parallel). Restoring the nvram calibration data resets this. Finding most data in the dump was relatively easy by comparing to battery statistics available through ThinkPad tools. I have detailed notes and posted to comments at above site.

There's some debate on different cell charging profiles as the original cells were 4.1v versus modern chemistry being 4.2v and so potentially will end up undercharged... but I've had great success just dropping in and don't feel the need to squeeze out more capacity.

Took an afternoon to do....not necessarily worth it, but was a fun project to figure out. My 9-cell is back to 10 hours of runtime/way better than any aftermarket I've tried.

That's much more of an explanation than I expected from my comment, thank you very much!

Reading between the lines, I think you've confirmed what I figured I had to do to replace the cells in my X230 - apply voltage across each of the cells as I swap them out, so the chip doesn't lock down.

But now I'm wondering if I can simply get a busted X220 battery to repair and use in my X230. The first search result says that it fits, but the X230 won't charge it due to DRM crap. But it also mentions a modded BIOS to get around this, and I'm running coreboot, so it seems that avenue might still be open - assuming it's really the "BIOS" and not the EC (embedded controller) chip checking.

BTW is gutting power tool batteries really a practical way to obtain reliable 18650 cells? It seems like that would be an expensive source, even on sale. But I admit my experience is with Dewalt 20V, which have their own premium. I figured I'd be hitting up the vape community to see their recommended sources when I got down to it.

While swapping cells, just be careful to match voltage and severely limit current to avoid any danger/excitement. Sure you can find some forum posts on this. Also, the new and old cells must be brought very close in voltage as discrepancies are flagged disabling the battery. This also goes for between cells but allowable differences are larger. I think this battery has 3s3p configuration.

I've bought quality 18650 cells online 10 for about $100CAD for a x220 battery rebuild. More recently got 2x 2Ah 18v Ryobi packs which yeilded 10x cells total for $29CAD on clearance at Home Depot....