What are Marine Cranking Amps (MCA’s)?

MCA is the commonly used rating for marine/RV starting power. It is the number of amperes a lead acid battery at 32° F (0 ° C) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery). This lets you know how much power you have to start your boat’s engine.

What are Amp Hours?

This rating applies to deep cycle marine batteries. Amp hours are simply a unit of measure for a battery’s electrical storage capacity. This is obtained by multiplying the current in amperes by the time in hours of discharge. For example: A battery delivering 5 amperes for 20 hours, delivers 5 amperes x 20 hours = 100 Amp Hr of capacity.

This rating lets you know how many amps, for how long, you can draw from your deep cycle battery.

What are 'Deep Cycle' Batteries?

These batteries are designed to provide deep cycle power and that makes them very different from ordinary car batteries. Deep cycle batteries supply a relatively low amount of current for a long period of time. They are specially designed to power electric trolling motors and other electrical accessories in boats and recreational vehicles. Unlike ordinary car batteries, they can be run down and recharged (deep cycled) repeatedly with minimum loss of capacity.

When a car battery is deep cycled, it looses capacity very rapidly. This limitation makes car batteries a poor investment when used for marine and RV deep cycle applications. A single deep cycle marine/RV battery will outlast 2-4 car batteries.

Are 'Deep Cycle' Batteries Constructed Differently?

Yes! Deep Cycle batteries specially designed with denser active material and thicker plates to withstand deep discharge-recharge service. They are also reinforced by envelope and glass mat separators to reduce shedding of the active material and damage from the jolting vibration of a boat on choppy water.

Car batteries on the other hand, use porous active material and thin plates so that high-amp energy can be quickly delivered for maximum starting power. Repeated cycling weakens the positive plates and makes the active material shed from the grids. They are not built to withstand the heavy buffeting experienced by marine batteries. They are simply designed to do a different job.

Where can I use a deep cycle battery?

Deep Cycle batteries can be used wherever the battery is continually discharged for an extended period of time, and then recharged:

  1. In boats for powering trolling motors, fish finders, depth finders, lighting and other accessories.
  2. In motor homes, travel trailers and tent campers to run accessories, radios, TV’s, fans, refrigerators etc.
  3. In outboards and sailboats to power lights and accessories.

How long will a deep cycle battery last?

The maximum service life and performance of a deep cycle battery will depend on how often if is used and how well it is maintained, including recharges. Batteries that are rated in the cycle life should deliver that number of cycles. Cycles are defined as one complete discharge and recharge. If the battery meets the daily usage requirements, you can assume that you will get one day of use for each cycle the battery is rated at. This may not apply if your battery is stored for long periods of time or if it is not well maintained.

How can I tell if my battery is charged?

The battery’s state of charge can be tested using a hydrometer or a voltmeter. A hydrometer will determine the specific gravity of the electrolyte in each cell, while a voltmeter will give you a voltage reading. There are some batteries that come with a state-of-charge indicator eye built in the battery’s cover.

Do I need a special charger for a deep cycle battery?

No, but properly charging a deep cycle battery is a very important factor, which can affect battery performance and life.

What is the best way to charge my deep cycle battery?

The electrical capacity of the battery charger determines how long it will take to charge your battery. In most applications, a 10-25 amp charger is recommended.

  1. Determine the battery’s state of charge using a hydrometer, voltmeter or state-of-charge indicator.
  2. Check electrolyte level before charging. Add distilled or good quality drinking water if the electrolyte level is below top of the plates.
  3. Follow the instructions provided with the charger. There are many chargers on the market, each with their own features.
  4. Be sure the battery is completely recharged. Use a hydrometer to determine the % of charge, following the manufacturer’s instructions.
  5. Recharge within 24 hours after each use. Discharged batteries can freeze.
  6. Do not overcharge your battery. Overcharging causes grid corrosion and reduces battery life. A charger with a timer switch is best.
  7. Do not use a fast boost charger. A slow charge is best for a deep cycle battery.
  8. Unhook the charger when the battery is fully charged. 

Can you overcharge a deep cycle battery?

Overcharging a battery occurs when the battery remains on charge after it has reached full charge. Overcharging causes excess heat that can cause the plates within the cells to buckle and shed their active material.

Is my marine battery 'maintenance free'?

While your battery is maintenance-free, it is also maintenance accessible. For optimal performance, the electrolyte level should be maintained between the top of the plates and the bottom of the vent car openings.

What is the proper way to store marine batteries?

Clean battery cases and terminals with baking soda and water, being careful to make sure the solution does not get into the battery. Always check to ensure the battery is fully charged before storing. Batteries stored in a discharged state are susceptible to freezing and an increased rate of further discharge. Store in a cool dry place and out of reach of children and pets. Check the state of charge every 45-60 days and add distilled water if needed.

(Portions of information from Battery Council International/BCI