Boat Batteries

The source of DC power is usually one or more marine-grade batteries, normally 12 volts each. They are similar to automobile batteries, except sturdier—and of course more expensive.

These powerful DC batteries can be classified into two major categories: Lead Acid and Lithium-Ion

• Lead Acid
  • Wet or flooded batteries that contain lead plates in a mixture of distilled water and sulfuric acid. These were common for many years but are rarely used these days because must be serviced regularly to ensure the acid levels are kept full. If they are low, top up with distilled water or collected rainwater only.
  • Batteries containing a gel material, instead of liquid, are sealed and thus minimal service is required.
  • Absorbed glass mat (AGM) that uses micro fiberglass. These represent the latest state of the art in lead acid batteries and are generally more expensive but tend to last the longest.
  • Lead Acid batteries last longer if they are kept constanty fully charged. Consistent cycling to low voltage and recharging can shorten the life significantly. For this reason, it is a good idea keep your batteries “on-charge” when you are away from your boat. Use a shore power connection or  “trickle” charge your batteries using a small solar panel.
• Lithium-Ion
  • There are various chemical makeups of Lithium-Ion and new ones are being invented daily.
  • Lithium-ion batteries are very expensive but tend to last longer
  • The energy density per size and weight of Lithium-Ion batteries are multitudes better than Lead-Acid
  • Lithium-ion is slowly infusing into the marine market because of its many advantages (except cost (for now))
  • Lithium Ion batteries also do not like having their charge depleted – but they also do not like always being constantly held charged to 100%. They like a range of 80% to 50% charge to give a longer life. Given the cost of Lithium Ion, ensure you have a professionally connected controller to maintain appropriate charge
  • BE EXTREMELY CAREFUL with Lithium Ion batteries if connecting together. There is a huge amount of energy in each battery that will immediately start flowing if the batteries are not at a similar voltage. Charge the batteries first to be less than 1/2 volt difference before connecting together.

Since batteries are often networked together, it is suggested that you use only one category type of battery above on your vessel. This will aid in extending the life of your batteries.

All batteries tend to be heavy, so they should be firmly secured low in the vessel, under a settee near the vessel’s center.

DC Battery

Sometimes, in order to double the amount of overall available energy to the boat, two batteries are wired together. If you wire two batteries together, to keep the same voltage (not blow things up) you must do so “in parallel.” This means positive on one battery to positive on the other battery and negative to negative. This keeps the output voltage at 12 volts. Wiring “in series” will result in 24 volts, which will blow up your circuits and bulbs and bilge pumps and who knows what else.

Parallel and Series Wired Batteries.