CVO 10/7/2012First, check the battery and starter cables for their tightness or free of corrosion and physical damaged.
A 3/4 charge battery is 12.50 volts
A discharge battery is 11.75 volts.
A battery under a cranking load and it is reading less than 7 volts,it will be a recycled ( junk ) battery.
The alternator output must deliver a good voltage between 13.5 to 14.5 volts in order to charge the battery.
Local auto parts stores will test this vehicle charging system for free of charge.
Note: in the event, if the vehicle succeed to all the requirements above, see this link How to Stop Car Battery Drains: DIY Auto