The same problem happened to me with my Duo 280c. I had to do this procedure many times before succeeding: 1) reset the Power Manager; 2) boot the PowerBook without battery; 3) when Mac OS starts loading the extensions, insert the battery.

I had to do that many times, because at first the PowerBook just shut down when I inserted the battery. Then, after many attempts, the boot completed with the battery in. Since then, I keep the duo plugged with the AC adapter.

Cheers

Rick