I have yet to fully understand voltage and such with computers (I understand none of it, and quite honestly, it's an alien language to me). But I commonly see issues like this.
This may be that the battery has gone and decided that it wants to be a paperweight now, basically, it's dead, dead dead.
Usually I test this by removing the battery and seeing how the computer responds if I try plugging in a battery from another device. (Helps when one has dozens of the same model for spare parts.)
If the other battery holds a charge? Great! It's the battery. If it's the same issue? Well then, the chances of this spare battery going from fully functioning to paperweight in 5 minutes is unlikely.
Another thing you may be able to try, ''not all computers'' can do this. Unplug the battery and remove it, plug in the charger. Does it turn on? Or does the computer remain an expensive paperweight? If it does turn on, see if you can go and find the battery settings and such. If you do, it's probably freaking out, I've had it display anything from '250% charged' to '0%' and 'N/A'.
This should be able to at least rule out, the charging port works. This narrows it down to your battery and the area on the motherboard that is around the battery.
Sadly this is all I can suggest, good luck.