I'm not talking about the battery, but about the power pack. Then again, English is not my mother tongue... I mean the thing which sits between power outlet and laptop, that converts voltages. And that is safe to combine.

Also, I found what I was looking for: HP does indeed use another ttype of plug, one with 3 contacts, whereas the ASUS one uses only two. The central PIN on the HP plug is there so the laptop can sense what amount of power the power pack is able to divert to charging the battery. That signal can be emulated by either putting a 22kOhm resistor between plus and the signal pin (resulting in the battery not being charged at all - doesn't matter to me, as I said, it's dead) or using a 500kOhm potentiometer to regulate battery charging power manually. It seems the area where it charges is somewhere between 200 and 300 kOhm.

It worked!

I used a 27kOhm R, and the laptop's up and running. Hope it doesn't crash anytime soon, or go up in flames.

Oh, so it's the transformer. Well, that's not too safe either, unless you know what you are doing.

Same voltage, same max current, so it's safe. (Assuming neither company lied about the stats.)

PS: The laptop's been running for almost 24hrs now. So, well, this looks [SOLVED]

Congrats on the fix! And sorry I was out of the loop for a bit, I was off and had important stuff to do