About Batteries


Take your time and do a little bit of homework before selecting marine batteries. Making the right choice eliminates many hazards and worries!


Have you ever wondered why there are so many different sizes or types of batteries? Did you know that every battery serves a specific functionality? This is especially true with marine batteries – and additionally, every boat is unique and has different power requirements. Our knowledgeable mechanical team at Ferry Point Marina & Yachtyard has  assembled some helpful information to help you understand more about keeping your battery in tip-top shape. Let’s dive in, shall we?

12 volt marine batteries are historically grouped into two different styles, the cranking battery (also known as marine cranking amp or MCA/CA) and the deep cycle (or “house”) battery.

  • The cranking battery is designed specifically for short-cycle intense bursts, such as starting an engine.
  • The deep cycle battery (pictured at right) was intended for the long haul and extended periods, for use running electrical accessories such as marine electronics (fish-finders, radios, and GPS).
  • There is a third new modern hybrid, the dual-purpose battery which, through the years, has evolved to cover both chores economically and efficiently.

Additionally, marine batteries can be categorized as wet cell, gel, or absorbed glass mat (AGM), according to the conductive material used within the battery.

  • The traditional, “old school” wet cell battery that contains battery acid (sulfuric acid with water) was once most popular because it was less expensive, while durable and light-weight. By today’s standards, these batteries are perceived as high-maintenance with many limitations. They need to be kept in a vented and accessible area, to be regularly inspected and topped off with distilled water, and they have a shorter life (about 30 months). Popularity for this battery is quickly waning with the advent of newer, improved and sealed batteries.
  • Gel batteries, which emerged in the late ‘80s and early 90s, contain a liquid electrolyte that is gelled with silicates then sealed. They are shock resistant, tolerate low temperatures well, and can be stored for longer periods without being recharged. Unfortunately, they also have limitations – most notably that they can run the risk of being overcharged by conventional chargers. Their charge limit is 14.1 Volts. If this happens, they will dry up and crack, and cannot be repaired. Gel batteries have been superseded in price, efficiency and capability by AGM Batteries
  • AGM batteries (pictured below), the newest variety, contain a dense filling of absorbent glass matting that is saturated with an acid electrolyte. This battery originally emerged from the aircraft industry and was designed to be shock and vibration resistant; it can safely function when mounted on its side.  As sealed units, they do not require refilling.  Also, overcharging of the AGM occurs only through occasional equipment failure, and not through misuse of chargers.

For Gel and AGM batteries, the popular advertising term, “maintenance free,” is a misnomer, it merely means that you won’t need to add water, as you would with wet cell batteries. You will still want to have someone perform regular functional testing and equipment check-ups.


AGM Batteries

AGM technology became popular in the early 1980s as a sealed lead acid battery for military aircraft, to reduce weight and improve reliability. (Photo courtesy of eastpennmanufacturing.com.


Mark Miller

Mark Miller, Mechanical Department Manager

At Ferry Point Marina, we recommend that all boats have at least two 31 Series AGMs. If a boat needs more amp hours, additional batteries can be added. By far, we find that this combination is the best and most efficient available, providing the most power for the least boat space consumed.  In addition, alternating between the two batteries will extend their lives significantly.

One tip that our Mechanical Manager, Mark Miller, shares is that when using twin batteries, use the even-numbered battery on even days and the odd-numbered battery on odd days. This will help you to remember which was used last, ensuring consistent and metered usage, while also allowing a “rest.”

As with so many other things in life, it’s a really good idea to take your time and do a little bit of homework before selecting a battery. Making the right choice eliminates many worries. Don’t wait for a beautiful day with family in tow, only to find that your batteries are not working. Have your battery system evaluated by our qualified marine electricians at “no charge,” (pun intended!)  They’ll be happy to make recommendations, according to the size of your boat and your own individual requirements. Our team feels that even the smallest boat can be customized to be worry-free, ensuring that you have full confidence and can enjoy your time on the bay!

Would you like for our team to take a look at your batteries? 

  Or call: 410.544.6368

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