A look inside a Ryobi 1.3Ah 18V lithium battery pack.

Having seen Julian Ilett dismember a larger version of the lithium battery pack used with the Ryobi one-plus power tool range, I decided to have a look inside one of my own. Especially when I'd just bought a cordless circular saw and wanted to see how the battery pack could handle the power requirements of a fairly high current tool. It's worth noting that the cordless circular saw is designed for simple cuts of sheet wood and not for full-on continuous industrial use.
Inside is a surprisingly simple array of just five 18650 style cells with beefy interconnects and a control PCB for handling the charge/discharge requirements of lithium cells.
If you could source decent known-quality cells capable of super high current then there's no obvious reason you couldn't fit an old or faulty battery pack with a set of new cells.
Julian's teardown of a higher capacity pack differs from this one in that it uses five clusters of two paralleled cells to give a higher capacity, but just treats each pair of cells as a single cell.