or just buy a minipc for $130 from Ebay.

It is frustrating though, I have several old phones that are in good shape. It would be nice to give them a job. There might be one or two that boot without a battery.

it happens to every one of them eventually. Wonder what really causes it?

I think there is a way to fool it by soldering a jumper on the battery contacts. Probably varies from phone-to-phone.