Back in the 80's, portable x-ray machines used HUGE NiCd packs to power them. I had to do the 6 month maintenance on them by cycling the batteries. From what I recall, they were 144 VDC packs. We would hook a large bank of lights to the cells and let it run them for 24 hours until the filaments would not glow. This basically killed the pack to dead.
Then, we would take the packs apart, remove the bus bars, check the voltage (0.2V or less) and hook variable power resistors to the cells. Dial up about a 4 amp discharge and keep dropping the resistance until it was at zero ohms. To make sure, we would jump across the cells with cables to give it a dead short. Then we waited another 24 hours to make sure those monster NiCd cells were DEAD!
The next day, we would remove the shorting cables and start bolting the bus bars back on the batteries. Once it was back together, we hooked the charger to it and watch the voltage start rolling back up. As a precaution, we replaced the packs every 5 years although they worked great with conditioning. Once a month, they would run the portable around the hospital to kill the batteries... sometimes they did not make it back so a forklift was called in. Those packs weighed well over 150 pounds and were a mother to move.
Defib batteries were brought back to life by... well... defibbing them to "wake them up". Now we use Cadex conditioners for those defib batteries and portable x-ray units use Hawker AGM cells so no more screwing around with mega-NiCd packs. That was why I would absolutely KILL my shaver NiCd's... it was much faster and they did last 11 years.
Warning to kids at home! DON'T mess with giant NiCd packs unless you have a blast apron, face shield, detailed proceedures and insulated wrenches. Oh yeah, I did not defib batteries... the Physio Control guy did that stunt. I did do something called "ride the lightning" though (I won't tell you)
Sadly, those days are gone and NiMH/Li-Ion does not like playing those games