Under what conditions did you measure this voltage?
If you measured 10.5 "at the coil" and you are using an ignition system with a ballast resistor, that could be perfectly normal
We need more info
What are you using for an ignition?
Did you measure the battery voltage running? At what RPM?
In addition to the running voltage at the battery, you also need to measure voltage, running and charging, at the starter relay "big stud."
How 'bout the battery condition? Has the car been sitting? Battery could be going bad, or just needs charged.
Lots of variables here.
