If the voltage is running away, this isn't a battery problem; it's either a regulator problem or an internal regulation (excitation) problem. A battery with an internal short may take an increasing current, but not an increasing voltage. The voltage regulator, internal or external, determines what voltage output is possible. Regardless of the current demand on the alternator, that voltage should never vary outside the tolerances prescribed by the voltage regulator.
Either the regulator is being fed too much field current by the regulator, or it has an internal short in the field winding or winding to case, but if you have verified that the regulator is good, then you're left with the alternator.
Incorrect placement of the field wire on the alternator will also create a similiar problem.
You're probably using a repackaged ford regulator; it's an automotive regulator with a different data tag on it, and they aren't known for their high quality, longevity, nor excellence out of the box. I've seen several of them bad right out of the box. The only difference between what you're sold, and what you buy from an auto parts store is the data tag, and the price. Generally about five times the cost for the "aircraft" part.
Again, if you're not seeing a runaway current, then you've got an excitation issue going on Improper internal wiring may well be the case, or you've got something else delivering voltage directly off the battery without proper regulation in place.