Two Battery Charger related questions

I purchased a Black and Decker Battery Charger that charges two different voltages of batteries; it charges both 12V, and 18V batteries.

I checked the output voltage of the charger itself, and it's output is 47 volts continuous.

How does that work, does the battery size become the limiter as to how much voltage it will receive, or does the charger reduce it's output, based on battery capacity, during the charging cycle?

I have another question as well.
I have a 24 volt DC power tool, that had a 500mA charger that doesn't work anymore. Can I use a different charger, that has a much higher amp rating instead, without damaging the power tool?

Thanks,
Gary

 

1. chargers are generally constant current devices, open circuit voltage is not very meaningfull. ( for lead acid chargers there is generally a constant current or current limited mode and a constant voltage mode )

2. faster changing usually results in shorter battery life, esp if the battery is overchanged. Some chargers are quite smart and will sense when it is time to stop charging. Even current is not the best way of characterizing the charger. Google chargers it will tell all.