A battery management system overrides the alternator’s voltage regulator and increases voltage at the batteries. With the rise in popularity of the Trojan/Crown/US Batteries with a ~14.8V recommended charging voltage fitting an external adjustable voltage regulator is highly recommended.
There are several brands available and I generally recommend and fit the Adverc system: they’re well made, simple, reliable & made in the UK. I will fit and work on whatever system you want such as Mastervolt Alpha & Balmar systems – & have the Mastervolt Interface for setting up properly.
If you think you have a problem with a Battery Management system or any charging or electrical problem on a narrowboat I’m happy to help.
Good prices given for 2nd hand Adverc controllers.