Battery recyclers use reconditioners to restore old rechargeable batteries once they no longer hold a charge. This DIY reconditioner can squeeze more life out of dead rechargeables and save them from the landfill.
To recondition a rechargeable battery, you have to discharge it rapidly, then slowly squeeze every bit out of it before attempting to recharge it. Msuzuki777's battery reconditioner uses an Arduino, some spare parts, and basic electrical theory to automate that process.
This particular reconditioner only works with AA and AAA rechargeables, but the design could be modified for mobile phone batteries or any others you may have lying around. It may not save time, but it's a DIY project that will definitely save money.