So I have been thinking a lot about the battery system onboard my classic yacht. There are so many different options! However, I have settled on a plan, and I hope it might come in useful to someone else out there!

So here it is and some of the choices I have made I am hoping to clarify!


Wiring Diagram Starting:Charging Scheamatic Also available as a PDF!  MY LADY Battery:Charging Diagram


The Domestic Bank, which is made up of two 110ah Exide Batteries are cheap, ‘Maintenance free’ batteries. I chose these on the basis of two things. First they are likely to get discharged and damaged as they are the domestic batteries! It doesn’t matter what battery you use this will happen at some point, no one is perfect! I believe it is more cost effective to expect to replace a cheap set every few years than replace an expensive bank every 5! The Domestic bank will be protected by a Battery Protect device from Victron energy. This will automatically cut the bank out to protect it from damage due to low voltage or high voltage and gives the crew an audible warning to either disconnect the load or change to the emergency bank.


The Victron Energy Battery Protect

The Emergency bank, which is an AGM technology battery will likely come from optima batteries, one of their blue top range, a dual purpose marine battery, meaning it can be used to start or deep cycle. The big advantage is a no spill battery and a low rate of self discharge. As it will stay un used for the majority of the time the extra expense is worth it i believe. I expect 5 years out of the emergency bank.


Optima Battery, Blue tops for marine use, the dark grey case indicates a starting/Deep cycle battery. Light grey case a Deep cycle only

The Starting Bank, is a very small dedicated starting battery with high cranking amps for its size. I am using a ODDESSY battery, of only 17ah. Astonishing battery it will crank over a huge 6 cylinder engine with no problem, all be it for a short time. I am using it on my yanmar 2gm20 so I am well within its capabilities, and only expect it to flash up the engine not crank for long periods. Hence the introduction of the emergency bank for redundancy.




The switching system is rigged as such I can choose where the domestic or starting load goes to. In an emergency, I can cut a faulty battery out entirely. A very useful feature.


Charging is achieved in two ways

First the 12v Alternator; an 50amp upgrade from the original, is fitted with a Advanced alternator regulator from Sterling. This changes the charging output from the alternator to a modern 4 stage charger, Cutting down charging times and fuel costs.


Sterling Advanced Alternator Regualtor

The Regulator works in conjunction with a Pro Split R 0.0 drop unit from Sterling. This takes the charge from the alternator and distributes it intelligently to the three battery banks without joining them together. This eliminates the chance of discharge by linking the banks of batteries together manually, a very useful feature.


Pro Split R, Available in many different options. Pictured is the 120amp 3 output version.

There is an emergency link fitted incase of failure of this unit.

The Battery charger System is serviced by two chargers. Both are waterproof units. I have chosen a Sterling Pro Sport 8 amp charger for charging the domestic and emergency battery banks. This float charges both of the AGM banks. and means the charge profiles are done correctly.

The domestic bank is charged by a Victron energy IP68 Charger. This charger is responsible only for this bank and is 25amp capacity. This will keep up with my expected normal domestic load when the heater, lighting and pumps are running.


The most economical way of fusing the high load circuits i have found, which is still of good quality is the Blue Sea Systems AMG fuse Block also referred to as a MEGA Block. I have kept to the same fuse block for all batteries as i wanted to ensure the spares were kept consistant!


All other circuits on the domestic load are protected by circuit breakers.