original charger failed so I purchased a replacement for my Gateway M6755 laptop. I plugged the adapter into the laptop but never turned it on. When I started putting it in the case, I noticed the battery was extremely hot. The adapter was charging the battery I think.
I'm guessing a cheap and probably Chinese clone of a proper charging unit. You have to aim for the more expensive equipment where electricity is concerned. It might not just be your laptop that burns up - the whole house could go with it.
Make sure you buy the unit with Voltage and Ampereage figures match those on the battery; not just the one with the plug that fits.