Do you have an old laptop whose battery struggles to reach 30 minutes? I used to.
An aftermarket 6-cell pack would have cost me around $40, which isn’t expensive, but the laptop was old (circa 2006) and not worth putting money into. I happened to have a fair number of Lithium-Ion battery cells “lying around”, and decided to upgrade my pack, not just with new cells, but with more cells.
This project was completed about a year ago, and I’m surprised I never posted it before!