clueless eBay seller for today is:

[Jay West]

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...

or

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.

Jay