I am the proud owner of a new very old laptop, which comes with two very old NiCad 9.6V 2400mAh battery packs. Toshiba PA8708U, if you care.
The power supply appears to be failing (it won't turn on), but it is charging the batteries --- so I let it do that for an hour or so. One of the batteries, from stone dead, has charged to about 12V. The other is at about 10V. The voltage being produced by the charging terminals is 15V.
I know that NiCads tend to charge at fairly high voltage and are current-limited, but I wouldn't expect the battery voltage itself (while disconnected from the charger!) to go above the rated 9.6V.
So I am deeply suspicious. Is this normal behaviour? Does it indicate that the PSU is overvolting the batteries? Will they catch fire?
(The batteries are now safely disconnected, BTW.)