I've done this countless times with faulty chargers. It will certainly NOT melt your battery.
If it's like 2 watt your battery can radiate off the extra heat but if it's at like 10 watts over you're definately breaking it.
What would stop me from using a 4000 watt charger to charge my laptop in 2 seconds?
Source: study electronic physics at uni
EDIT: wattage is voltage times current. You can make the current 5 quadrillion amps, but the device will only draw what it needs. If you make the voltage 5 quadrillion volts your laptop would explode in a blaze of fiery glory. Since de adapters convert from ac to dc because you can't charge batteries with ac there's a transformer in there along with a rectifier; the transformer lowers the voltage but amps up the amperage. The amps don't matter like I said before, it's the voltage that does.
20volt*5amp=100w = baseline
40volt*5amp=200w = broken stuff
40volt*2.5amp=100w = 100w but still broken stuff
20volt*10amp=200w = fine
Since the main thing that is changed around in adapters is voltage and not amperage, most higher wattage adapters would forget your device up.
Depending on the wattage difference to what the device is rated to, you're just changing the speed at which you're killing your laptop. If it's twice the rated amount it's gonna be dead soon. If it's a couple watts more you're just slowly shortening it's lifespan, like Pastrey Crust is doing. Of course there's a couple watts of marigin, but that's just a couple.
The best thing to do is look up what voltage and amperage your laptop needs, and buy a new charger with exactly those specs. Odds are the charger is not supplying enough voltage because it's old or broken, which leads to the laptop drawing more amperage, which makes it not work and overheat.
