I do a similar trick using a 10,000 uF, 40 volt capacitor charged (via a resistor) to 13.8 volts and then discharged a couple of times (without the resistor) into the battery.
Cheap 'n dirty but has revived loads of batteries.
This removes the whisker that causes the "won't charge" issue.
This will sound very facetious but I don't think I can walk into Tescos and buy a 10KV supply, but what I can buy is one of these fly killing 'tennis rackets' that kill by zapping the fly with very high voltage, low current when you swipe them and they hit the wires. If I 'swiped' my expensive but useless rechargeables with it, would that work?
Edit: I am pretty sure a ignition coil would work also. Also, this won't work on LithiumIon's. The high voltage can damage short protection circuits inside some drill or phone battery's also.
I cheep & easy possibility is to connect a wall wart transformer backwards to mains to get a few KV. The problem is it will saturate to you must switch the mains on then off before it burns/arcs itself to destruction.
I rejuvenated NiCds back in the '70s by connecting them across a car battery with a headlamp bulb in series. Does anyone still use NiCds? I haven't seen one for years. Everything uses Nickel Metal Hydride cells nowadays.