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Weird battery issue Dell XPS L702x


So I've just brought a new battery for my L702x (I've been running it without one for the last 4 months).

The battery shows that it has 88% charge when plugged into the computer, but it doesn't charge, nor does the computer work off the battery. If I unplug the adapter the computer just dies.


When I got the battery it worked and I charged it too 100% (When I got it was at 70% or something). When I did my first test once the battery dropped to 88% the whole computer just died.

Power button didn't work anymore. When I plugged the adapter back in it booted with angry warning to turn my laptop off immediately because the battery was overheating and needed to cool down.

The battery was really really hot, so I powered off the laptop and took the battery out and left it to cool. The battery also has a rattle now, like something is come loose inside it.


Computer is working fine like always on mains power, no issues right now. I analysed the battery connector on the laptop to find the negative and positive terminals and the ground terminal that activates the battery

(this kind of laptop battery has I think mosphet protection and won't give or take charge unless a certain pin is shorted to ground on the connector. )

Once I figured out the correct pins and activated the battery it's only reading 0.6v once it stabilizes (definitely dead). But the batteries internal power indicator still lights up all lights to show a full charge.


What I think has happened is some protection circuit on the batteries pcb must have fried itself? preventing power from going in or out of the batteries main terminals. But I think the cells are still holding the 88% charge internally and the computer is still communicating to the battery over the serial data bus that monitors the internals of the battery because it still monitoring the cell voltage, serial number, make etc when the battery is plugged in.


Thats my theory.  Does this make sense?  Or might it be something else? I've never seen a laptop battery fail in this manner


I am returning the battery to the supplier as soon as I can, I don't have another compatible battery to validate against, but I used the same method to check a battery on a different laptop and it showed a normal voltage of 10.5v when activated.


Also, battery is a 90Wh 9cell R795X

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