Battery Basics

We’ve talked a lot about engines, but the initial source of power in all of our boats is the battery. The related wiring, fuses, circuit breakers and other components, and how they’re installed, are also hugely important. If you don’t pay attention to these components and all their corresponding details, you may not get the proper performance and enjoyment you expect from your rig.
Let’s look at batteries. Not too many years ago there was a 6-volt and then a 12- volt battery, with few choices as to sizes, ampere ratings, and specific applications. Today there is a large, confusing list of options available to us. Do we want a Group 24, Group 27, a deep- cycle, or a cranking battery? What amp rating is best, and what do the ampere ratings really tell us?
Most engines today, whether inboard, outboard, or stern drive, have specific battery needs to ensure proper performance. That performance is not just for starting the engine. With all the electronic components of today’s engines (injectors, ignition, fuel pumps, oil pumps, trim pumps, and electric/hydraulic power steering) significant electric power is needed to operate everything. When you total the engine’s basic requirements, you are often precariously close to, or actually below, the alternator output to the battery at low rpm. Add in your marine electronics, and you could be reaching well beyond your system’s capability. Idling all day offshore as you drift or troll may cause your battery to slowly discharge, dropping its available voltage below what the engine needs to run properly. In some engines, a minimum voltage reading of 10.5 is necessary just to keep the engine running. It might still turn the engine over and start it, but it may not have the energy to fire the ignition and supply fuel through the electronic injectors.

Keep ‘em Charged

Most of us understand that when we are buying a new or used boat, the batteries supplied may not necessarily be top-of-the-line. If they seem to do the job, we don’t think much about them. But in the warmer climates everyday heat is a major enemy of batteries, and can shorten their life considerably. In areas of the country that force us to put boats in storage for the winter, how the battery is cared for during this period is also critical to increasing life expectancy. It’s best to keep batteries on a regulated “trickle” charger to maintain charge while not in use. A battery that is not charged (and kept charged) can freeze in cold temperatures and a cracked case is the likely result.
 A battery is like a lot of things in life – use it or lose it! A car battery will typically last longer than a boat battery because the car is used regularly and the battery stays charged. When it comes to boats, the old adage of a battery’s life being two years is pretty well on the mark. You’ll usually get a heads-up when it’s about to give up on you, with the warning being a “dead” battery one morning or a bit slower cranking speed than you’re used to. You plug in the charger, the battery miraculously comes to life, and you’re off on your trip. You may think a light was left on, or that the radio memory pulled the voltage down. The reality may be that the battery is sulfating, plates are warped, and it no longer takes or holds a charge like it once did.

Choose Wisely

How do you determine what’s right as a replacement battery? If the battery’s primary purpose is to start and run the engine, you should check with your engine manufacturer (or owner’s manual) to determine the recommended CCA (Cold Cranking Amps) or MCA (Marine Cranking Amps). Much effort by the manufacturer has been put into sizing the battery output to the specific engine requirements, so buying a smaller battery solely based on price is asking for trouble. Obviously you need to make sure of the current battery dimensions to be sure the replacement will fit in the space and/or box. A Group 24 battery is pretty typical, but Group 27s are larger and aren’t as stretched to supply the power you need. If you have room for the bigger battery, although heavier, it may be a wise choice.
For today’s larger marine engines, a 750 CCA or 1000 MCA is typically the minimum recommendation for an engine cranking battery. These letters signify the Cold Cranking Amps and Marine Cranking Amp rating of a battery. CCA is the number of amps a lead acid cranking battery can deliver for 30 seconds at 0 degrees F, and maintain at least 1.2 volts per cell (7.2 volts on a 12V battery). MCA is virtually the same thing, except it’s the number of amps a battery can deliver in 30 seconds at 32 degrees F. You wouldn’t want to crank your engine for 30 seconds (tough on the starter) but that’s the basis for the test rating. Read the ratings on your prospective new battery carefully and get the size recommended, or even bigger, if you can. The higher rated, stronger battery will do the job better, and will do no damage to anything it powers. There’s no free lunch in a cheaper battery, so don’t pinch pennies here.

Deep Cycle vs. Cranking

If you have an electric trolling motor, thruster, windlass, or other battery powered accessories that draw larger amounts of current, you’ll want a separate deep cycle “house” battery for that purpose. A deep cycle battery is only meant to be used where high rates of discharging and re-charging occur often. A deep cycle battery is constructed differently than a cranking battery, with thicker, heavier plates. The longer, higher amperage requirements of trolling motors and windlasses, for example, would heat and distort the thinner plates of a normal cranking battery. The cranking battery has more yet thinner plates to give a fast voltage spike to crank an engine, but is not intended to maintain high power output for long periods. Yes, a deep cycle battery can be used to start your motor in a pinch, but a two- or three-battery system is highly recommended to separate the engine battery from the accessory (house) batteries.
The best way to be sure your battery is still good is to have it “load tested.” Most auto parts or battery specialty stores will load test your battery for free and tell you if it’s still serviceable. Just because it’s gone dead once or twice doesn’t necessarily mean it’s no good. The rest of your electrical and charging systems may need some attention as well, as something other than the battery itself may be the cause of the problem.
Bottom Line? Keep your batteries charged, keep the terminals clean, and by all means get out in the boat and “exercise” your electrical system as often as you can!

Content courtesy of Center Console Angler

Category: Sailing , Overnight Cruising