Replacing an Internal NiMh Battery Pack - Choosing Nickel Metal Hydride Batteries and Soldering

Warning: Heating any battery can cause chemical leakage, explosion, and injury. Please follow all battery manufacturers recommendations for safe handling and use. When replacing batteries use the correct part for your application.

I've had a shaver that uses an internal Nickel Metal Hydride (NiMh) that's stopped taking a charge. Tearing it down and testing out the battery pack showed it wasn't capable of holding a charge.

So I've decided to replace the battery pack! Without too many options for a AAA NiMh battery in my bin I compare some old Panasonics to new generic "1800mAh" batteries and come back with a (probably unsurprising) result.

The better batteries get soldered in place and I attempt to fire it back up. ... https://www.youtube.com/watch?v=EUtYOoCV9ls