Well Eddie,
 Now we are getting into the electrical engineering aspect. The boost mode doesn't increase voltage. It does increase amperage. That is how it gets the higher energy level. I have used 6V to charge an 8V battery, but it never produces more performance than a 6V battery, it just doesn't match the numbers. If you try to charge with a 12V charger, it is likely to warp the lead plates in the battery, and ruin the battery. Someone once told me of a way to charge 12V for so many minutes, then let it rest for so long, repeat, etc., I tried it, I bought a new battery. If need be, I have a variable voltage power supply that was made for mainframe computers years ago. It has a voltmeter and adjusting knob to set the voltage. Old technology, slow, but I have used it. My guess would be, you could charge your battery to 6V, that will get you started. Then check the voltage with a volt ohm meter set to DC volts. Check it at the battery terminal on the voltage regulator. Measure the size of the voltage regulator, just to make sure that is what you have. A cutout relay will be small, about the same size as a horn relay that mounts to the firewall on a vintage car. A voltage regulator will be bigger, at least twice that size. Another dead give away, a cutout relay will have one coil, and one set of contact points inside. A voltage regulator will have more than one. Let me know what you find.
Take care!
Andy