There is the GLOD phenomenon (Green Light of Death), caused in some PowerBooks by lack of charge in the backup battery, and confused power management software.
Did the cells you just installed come pre-charged, by any chance? Equill used to opine on here about this question, and regularly advised leaving a PB that you want to resurrect plugged in, even if apparently dead, for at least a couple of days before resorting to anything more drastic. I would go with that for now.
The PB150 is closely related to the Duo series, and the Duos certainly were afflicted by the GLOD problem. But it is found here and there in some machines, rather than in all machines — one of life's little mysteries, as it were. I say this because I have seen differences in different Duos in this regard with my own eyes, and because I have a PB150 that will boot with a dead backup battery, quite happily (and then charge it), but that does not mean that any old PB150 would do so.
You should try to get it going. It was a lowend product, but I personally share Trash's fondness for the machine: I find the screen good (for what it was), and can't understand why people complain about it; I like the RAM expansion possibilities; and having IDE rather than SCSI is, of course, a unique advantage in the thing. Mind you, if it won't boot, none of this is going to get a lot of use.
