Classic/Antique Car Repair: 10 Volt Battery, volt charger, lead acid battery

Question
The engine has an old 10 Volt system and battery. When charging the battery should I set the charger at 12 volt or 6 volt?  Also what amp level.  I know this is not specific to your area of expertise but I could not find anyone who was close.  Thought you might know.  Thanks

Answer
A battery charger usually puts out 2.33 volts per cell. that means that a charger for a 12 volt battery puts out 14 volts. A charger for a 6 volt system delivers about 7 volts. A charger for a 10 volt or 5 cell battery would deliver 11.5 volts. A 12 volt charger will over charge the 10 volt battery while a 6 volt charger will undercharge the battery. So neither will do the trick. Now, is this battery a lead acid battery like used in a car? Also do you have any idea what the battery capacity is and what is it's exact use? Let me know we might be able to work out something using a 12 volt charger and resistors.
Brad