sony d t401hello boom boom man. Glad to hear I finally found another dt 401 user.
You can charge nimh or nicd in your pcdc by strategically taping a shortened cotton Qtip to one of the batteries so that when it is inserted the Qtip will push the small triangular tab back as far as it will go to activate the charge circuit. Use cotton end to push tab.
It may take a little finaggling but I got mine to work just fine .
I'm using a pair of olympus nimh which fully charge in about 3 hours. They dont get as warm as they do in my olympus wall charger.
I'ts also possible that you could find an old sony battery pack at a recycle bin ie;radio shack or target, and remove the battery holder and insert new batteries.
Let me know and good luck.