The price of lithium-ion batteries has declined by 97% in the last three decades
Although Li-Ion cells are getting cheaper and cheaper every year, it still is worth salvaging the good ones from depleted laptop battery packs. When a laptop battery pack is gone it&#x27;s almost always the case of one, max two, 18650 elements that failed, not the whole pack. I&#x27;ve built some good power banks using empty shells (very cheap on Ebay, Aliexpress etc.) and fitting inside the good cells salvaged that way. They last just like new ones once one discards the bad ones.
The only caveat is that cells taken from laptop battery packs are not individually protected, that is, they don&#x27;t employ the small pcb containing a protection against excessive charge, discharge, temperature, short circuit, etc. because the needed circuitry is already contained in the laptop battery pack. Power bank shells do indeed contain such protection, so no problems, but care must be taken into insulating the cells contacts so they cannot short, and before fitting them the user must charge each of them to a known identical voltage, so that once they&#x27;re put in parallel (remember: no individual protection) the strongest ones won&#x27;t discharge their energy on weaker ones.