triage - the battery was from a name brand phone - definitely...

triage - the battery was from a name brand phone - definitely not a knock-off battery, and the charger was original.
The swelling was quite disconcerting - almost surprising that it hadn't popped the back off the phone. It is even more scary to think how Mrs niu had responded to the dodgy battery by repeatedly putting it back on the charger.

I have since found several articles on this phenomenon - apparently due to outgassing following overcharging.
https://www.tekrevue.com/swollen-battery/
"There are strict limits on how much current can be put through a lithium-ion cell. During normal charging, you never see metallic lithium, which is inherently unstable. But during overcharging, the lithium builds up faster than it can dissipate. The result is that metallic lithium plates up on the anode. At the same time, the cathode becomes an oxidizing agent and loses stability.
This reaction produces heat, which warms the gasses inside the battery, causing them to expand. Without any avenue for ventilation, the battery’s casing expands with the gasses, distorting and warping its appearance into that familiar swollen look."

Elsewhere I have read the gases are typically ethene, hydrogen, oxygen.. Oh dear.

Many of these articles offer very sensible advice

If you puncture the swollen battery, you’re in for a bad time as the compounds inside will react with the oxygen and moisture in the air.

"Above all else, be safe. Don’t try to puncture the battery,.."

"If you remove a battery and discover it’s already bulging, don’t mess with it. "

"...we strongly encourage you to call ahead and ask if the facility is equipped to accept a damaged battery and to check what the protocol is for bringing the battery in. Do not simply toss a swollen battery into a general battery recycling bin at your local big-box electronics store."



Nowhere do they suggest an attack with a spade on the front lawn...

So yes, roll on solid state. It is interesting to see that the latest Tesla semi and roadster announcements are being greeted with some doubts on the battery front. Perhaps solid state is closer than we think.