On the HP power supply and cheater plug...
I'm fairly certain, although not positive, that you can "fix" this problem.
A) Get a battery cheater plug. Of course that's the obvious answer. I think
it's a 1K resistor across pins 3 & 6. But...
B) I THINK that you can cleanly and effectively remove the battery backup
option from the HP power supply by opening the power supply and removing two
printed circuit cards. The power supply still works perfectly, just no
batter backup. I have never tried this, but I am quite sure that the battery
backup option could be added to a power supply which didn't include the
option. When you ordered this, you got two PCA's that went into the power
supply, plus the battery itself. So if you don't have the batter, and no
cheater plug, I think you could just remove the two PCA's and run fine.