Getting the zook ready for a trip to Fraser in the last few days (we leave tomorrow!!!

) We installed additional wiring to handle the fridge cos the standard just wouldn't cut it. When we tested the wirie up with a multi meter and the engine running, we found out that the alternator is belting about 16 volts back into the battery.
So I have a couple of questions...
This is a new battery and we will be on fraser for a week from tomorrow, is a weeks worth of driving around on the island enough to cook the battery with that sort of charge going back in?
I am guessing this is a voltage regulator problem. Are they a big headache item to replace in thsi vehicle?
Cheers
Zook