|What happened to the original AC adapter for the laptop ? |
If the AC adapter is putting out the proper voltage - 18.5 v - if the polarity of the voltage at the plug is correct - center positive , and if there's nothing wrong with the battery, then the plug that plugs into the laptop's jack should NOT get HOT.
Either you have a problem with the plug you're using, or with cord near that plug, or you have a problem with the jack or the jack's connection inside the laptop.
If the universal AC adapter has multiple plugs, the proper plug has the largest external diameter that will fit in the laptop's jack, and the smallest center hole that will fit over the center pin in the jack. The diameter of the center hole is more critical that the outside diameter - it that's too big you're likely to have problems charging the battery and powering the laptop on the AC adapter alone.
(DC plug) Connecter size:
Internal Diameter: 1.7mm
External Diameter: 4.8mm
If the battery gets HOT when the AC adapter is plugged in as I described, and if the AC adapter is putting out the proper voltage, it's polarity at the plug is correct, and if you're using the proper plug, it probably IS internally shorted, no matter how old it is !
For maximum battery charging capacity you should "calibrate" the battery.
HP Notebook PCs - Calibrating the Notebook Battery in Microsoft Windows 98, ME, XP, and 2000