My HP67 Has Melted!!!

[Ignatz]

Noticed that my HP67 seemed to be losing charge, even when switched off... plugged it in for a recharge. A bit later, turned the calc over, the battery door had buckled at the top from heat. Managed to remove the battery (only a few months old). It was hot to the touch... unplugged, let everything cool down, put a fresh battery in. A few hours later, back into the office to the smell of burning plastic... the battery door had melted!!! This battery was too hot to even hold. This morning, the hot battery is dead. Plugged in the first battery (the one that was warm and caused the buckling) to monitor the situation: calculator still functions (phew!) and, even after a few hours charging, the first battery is still cool to the touch.







Any idea what went on there?