![]() ![]() The code was shifted over to an ATtiny85, with a voltage divider wired up to one of the pins so it can read the pack voltage. He was slowed down a bit by an undocumented CRC check, but in the end he was able to come up with a fairly mature firmware that even allows you to provide a custom vendor name and model number for your pack. From there he wrote some Arduino code that would mimic a battery as a proof of concept. ![]() From a more practical standpoint, it also meant he’d be able to create a higher capacity battery pack than what was commercially available should he chose to.Ī logic analyzer wired in between one of the third party batteries and a spare T420 motherboard allowed to capture all the SMBus chatter between the two. Which from the sounds of it, wasn’t a very high bar. By reverse engineering how the battery pack communicated with the computer, he reasoned he would be able to come up with an open source firmware that worked at least as well as what the the third party ones are running. Which is why decided to take the road less traveled and scratch built a custom battery for his ThinkPad T420. You can often get two or three of the knock-offs for the same price as a single real battery, but they never last as long as the originals. ![]() Which means you also know how much legitimate OEM packs cost compared to the shady eBay clones. If you own a laptop that’s got a few years on the clock, you’ve probably contemplated getting a replacement battery for it.
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