In laptop battery packs (and some phone batteries), there's a chip within each cell which has a low voltage cutoff, and calibrates to the cell - for old laptop battery packs, the advice to gain a little more capacity, is to disable the battery protection in the OS, allowing it to drop to 0%, then charge. I believe the reasoning is that over time, the different cells in the battery packs differ in capability, and the chips inside them hold memory of a charge that the cells may no longer be capable of, causing the BMS to not charge the cells optimally. It's risky - it can kill an ailing cell within the pack, which stops the entire battery pack working, but this has worked for all of my old laptop batteries, if done very rarely - you can gain a few useful %. It can also cause the BMS to report a fault to the motherboard, shutting down all motherboard function - sometimes the motherboards cannot be revived (rare). I don't know if ebike batteries have similar chips in their cells, or if this course of action is at all wise: Losing a £400+ ebike battery is not worth the risk, compared to a relatively cheap laptop battery.