Battery Selection

The Deep cycle lead acid batteries can be divided into Flooded cell, Gel Type and AGM (Adsorbed Glass Mat) types. All Gel and AGM batteries are valve regulated batteries generally referred to as sealed. Flooded cell batteries are also available as sealed batteries. Recombinant Vent Plugs are available for regular flooded cell batteries giving them the benefits of valve regulated batteries. Gel and AGM batteries are much more expensive than the Flooded cell batteries.

I did a survey of 12 electric boat companies recently (Nov. 2008) to see what type of battery is used most frquently for electric powered boats. Trolling motor powered boats were not included in the survey. Trolling motors are most often powered by size 27. 12 volt flooded cell batteries. The following section provides the popularity of the battery type in my survey with the benefits and disadvantages of this type of Battery and the sizes generally employed

• Golf Cart Batteries - 4 out of 12 companies Used 6 volt GC2 size Golfcart batteries
  This battery type has excellent current rate characteristics, excellent cycle ratings and good dollar value.It does produce more hydrogen gas than sealed types
• Flooded Cell Batteries - 5 out of 12 companies used various sizes of 12 volt flooded batteries, but mostly 4D size. The advantages and disadvantages are the same as for golf cart batteries above.
• AGM Batteries - 3 out of 12 companies offered AGM Batteries. These batteries have very low discharge Rates, long life spans, low hydrogen gassing. Good current rates. The Battery will work while submerged without producing chlorine gas.
• Gel Batteries - 1 out of 12 companies used gel bateries.They have about the same benefits as the AGM batteries above.

Battery Installation

Some important Battery Installation consideration for Electric boats

• Battery Banks should be held within acid proof battery boxes or trays. These boxes or trays should be securely fastened in the boat compartment. These trays or boxes can be made of wood then covered with fiberglass cloth using epoxy resin. Its good practice to use acid resistent trays for "sealed" type batteries, because there is a good chance that the typical flooded cell batteries may eventually replace the sealed batteries due to high cost.
• Each battery should be securely attached to the battery tray or box.
• Cables should be attached to batteries with locknuts or hex nuts with lock washers. Wing nuts should not be used for high current carrying wires.
• All battery compartments must be vented to the outside of the boat. This is also true for sealed batteries which do release some hydrogen gas. The best way to assure positive ventilation is to use an ignition protected fan near the bottom of the compartment on the opposite side of the compartment from the upper vent. This fan should ideally be wired to turn on with the charger,
• Cover positive terminals with a rubber boot made for this purpose to protect against accidental shorting.

Battery Maintenance

Some important Battery Maintenace considerations

• Water levels must be watched closely. Refill with distilled water to the bottom of the filer tubes.
• Terminals should be clean and dry
• Use a charger that turns itself off then monitors the voltage for re-charging
• Don't mix different types of battery in a bank. Don't mix old and new batteries in a bank.
• Be sure to set charger for your type of batteries.
• Turn off the battery charger when working on a battery bank. Charging conditions create the greatest ammount of hydrogen gas. Some hydrogen gas is also produced when discharging batteries.
• Check battery bank conections periodically. Clean corrosion with a paste of baking soda and water.