Off-Season Marine Battery Care

Robert M. Hohman

Complete Battery Source, Inc.

One of the most frequently asked questions we receive at Complete Battery Source is “ What should I do with my marine batteries during the winter months?” Off- season battery care is perhaps the most important factor in getting the most service life from your batteries.

The worst thing to do is nothing at all. Batteries that are left with no type of winterization may survive to fish again, but will most likely be damaged to the point that performance and overall life will be drastically reduced. 

All batteries both wet and “dry” or AGM batteries lose a small percentage of charge everyday. When this occurs, a crystal like substance known as lead sulfate forms on the plates. These crystals reduce and even block the flow of energy through the battery. A partially sulfated battery will still charge and even show that it is fully charged; however, runtime and or cranking performance will be diminished. A sulfated battery can be recognized by it’s “swollen” appearance. The sides of these batteries will be noticeably bowed out. In more severe situations, the plastic case around the posts will appear to pushing up from the inside. 

Batteries that are left connected are even more prone to sulfating. Minute parasitic loads caused by electronics, fuel injection, and engine control systems increase the rate of discharge. Discharged batteries are also more likely to freeze during the winter months. While a fully charged battery will not freeze until the temperature drops to –38 degrees Fahrenheit, a fully discharged battery will freeze at 32 degrees Fahrenheit. Frozen batteries will often have cracked or split cases.

At the very minimum, batteries should be fully charged then completely disconnected and left in the boat for storage. These batteries should then be charged for twenty-four hours minimum before the first trip in the spring. Contrary to popular belief, storing the batteries in a heated environment is not beneficial.

Batteries are nothing more than a contained and controlled chemical reaction. As with any chemical reaction, heat increases it’s speed. In fact, a fully charged battery stored at a constant 78 degrees Fahrenheit will lose 80% of its charge within 45 days while the same battery stored at 32 degrees Fahrenheit will take many months to lose the same 80%.

Many fishermen will store their boats with their on-board chargers left on. This practice can have varying affects depending on the charger. Some chargers will merely charge the batteries, and then turn off, leading to a discharged battery. Others will switch to a lower amperage charge, but will eventually over charge, causing fluid loss and battery plate degradation, leading to premature failure. Batteries that have been over charged will sound hollow when their sides are tapped. You may also notice fluid in the battery box or tray. For batteries that have removable caps, a visual inspection will show that the fluid has dropped below the now exposed plates. If your only option is to use your on board charger, we recommend that you plug the charger in once per month for four to six hours.

The best method for maximizing battery life is to use a battery maintainer. These devices are very popular and many brands are available. As with any marine equipment all maintenance chargers are not created equal. At Complete Battery Source, we have found a charger manufactured by CTEK to be one of the most advanced and effective for charging and maintaining both traditional wet batteries and dry cell AGM types. A link to the CTEK website can be found on our website at www.CompleteBatterySource.com

The CTEK chargers range in price from $44.95 to $119.95. The CTEK chargers use a three step charging cycle, including a pulse maintenance mode to rid the battery of minor lead sulfate build up on the plates.

Before storing you batteries you should, if possible, check the fluid levels. The fluid should be just covering the plates but not touching the inner wall of the fill hole. If fluid addition is necessary use distilled water. 

Next fully charge your batteries using your normal charging method. After charging make certain that the top of the battery is clean and dry. If your boat is stored where no power is available, remove your batteries and take them to your garage or basement for storage. 

You can also maintain multiple batteries with one maintenance charger as long as they are of the same size and type. The batteries should be connected in parallel, meaning positive posts connected together and negative posts connected together. Connect the batteries together using #6 or larger wire with alligator clips or ring terminals. Connect the charger and you are finished for the season. The batteries will be ready to reinstall in the spring. 

If connecting the batteries in parallel is too complicated, or just too much trouble for you, a single small charger can be used for each battery, or one charger can be rotated from battery to battery every few weeks. The second method will obviously require more work on your part.

Following these relatively simple steps, you can get the maximum service life from your batteries and more trouble-free time on the water. 

As always, should you have any battery related needs or questions feel free to call or stop in to any of the five Complete Battery Source locations in Brighton, Detroit, Okemos, Ypsilanti, or Houghton Lake/ Prudenville.