there is lead in solder, a somewhat hazardous material.
don’t rub lead in your eyes or eat it, wash your hands if you are handling solder.
the laptop powers on only sometimes, even after replacing the battery :
the problem may be a loose dc adaptor (on the motherboard where the power cable plugs)
a soldering kit (solder, a 15watt soldering iron, wire, wire cutters, third hand) can be used
to additional solder with a wire the dc adaptor to the motherboard.
or the motherboard can be replaced.
_________________MB over and out