Why does charging cause a device to lose charge?

[Eric Stork]

Recently whenever I tried charging my old cellphone, I found plugging it in made it lose charge, not gain.

I am getting a new phone, just want to know what causes this and is it a sign of needing to replace or something fixable.

 

[ex_bubblehead]

That's a sure sign that the battery is beyond the end of its useful life. They don't last forever.

 

[hotaru.hino]

If you let the battery sit at 0% for an extended period of time, it basically dies and won't hold a charge. Or it could be the battery is that old and just won't hold a charge. In any case the fix is to replace the battery.