What is Three-Stage Charging?
Multistage charging ensures batteries receive optimum charging, but with minimal wear and tear, regulating the voltage and current delivered to the batteries in three automatic stages:

• BULK: Replaces 70-80% of the battery’s state of charge at the fastest possible rate.  During this stage the battery accepts as much charge as the battery can allow or the charge source can provide

• ABSORBTION: Replenishes the remaining 20-30% of charge, bringing the battery to a full charge at a slow, safe rate. 

• FLOAT:  Voltage is reduced and held constant in order to prevent damage and keep batteries at a full charge.

Basic single or dual step charging sources such as most engine alternators, cheap battery chargers and basic solar regulators will only recharge the battery to 70-80% SOC, which means 20-30% of your battery capacity is wasted.  For example a 100Ah battery recharged by an engines alternator means the battery’s state of charge will only ever be around 70-80% SOC now consider the 50% SOC discharge rule, this means from the 100Ah battery there is only 20-30Ahs of usable capacity, so much for saving a few bucks and buying a cheap battery charger when additional batteries may have to be purchased to make up the capacity short fall.

There are many charge sources available to recharge batteries and depending on the application several may be used in a system to give back up or redundancy.

What battery charge sources are available?
Smart Battery Charger – The real heart of your electrical charging system is a smart battery charger, and is often overlooked by most people with the least amount of investment made in this area.

Cheap automotive style battery chargers (as described in the example above) just don’t make the grade when charging large house banks.  They will generally only charge a battery to around 80% of capacity and because of their small outputs they can take very long times to recharge if at all.  They can also damage batteries by overcharging or charging batteries at too higher voltage and they do not properly float batteries. 

When it rains or is overcast you cannot wholly rely on a solar system to fully charge your batteries, however a smart battery charger will do so nearly every time (if 240VAC mains  or AC generator power is provided for sufficient periods and the battery charger is sized to your system properly).  As a general rule of thumb the size a battery charger needs to be a minimum of 25 to 40% of your battery banks capacity.

AC generator either a main unit or portable – Is often the most efficient means of recharging batteries.  Running an AC generator provides the fastest, most accurate charging rate if used through a smart battery charger.  For example a small AC Generator such as a Honda EU10 can deliver up to 40amps of charging when used with a smart battery charger such as a Xantrex Truecharge 40.  Obviously larger generators have the ability to drive larger battery chargers which can speed up charging times and minimise generator run time.

Obviously the AC generator’s prime use in most cases is to provide electricity to the boats 240V system.  Careful consideration to genset needs to be taken into account such as size (KVA), Voltage, Hertz, physical dimensions, operating RPM, weight and sine wave output