It depends on what voltage the internal battery is. If it's a 6 volt, the charging voltage will be a little higher, close to 6.5 to 7 volts. Most of these spotlights are 6 volt. New batteries can be found at Battery International: http://batteryinternational.com/spotlight-batteries-vector-battery.html

You can see what many batteries you need at http://www.battery-stores.net/

It uses two 12 volt 6 amp hour, non-spillable sealed, lead acid, recarchable batteries