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Battery maintenance

By Bernard Bélisle <>

Many users of outboard electric trolling motors notice that their batteries do not last as long as they are supposed to. This is not a surprise, because many of them do not know the difference between a marine battery and a deep cycle battery, and few know the proper maintenance they have to perform on their batteries. Here is what you always wanted to know about this subject.

The world of lead/acid batteries is a very particular domain where many hunters, fishermen or even sailors are mixed up. In the following article I will try to provide answers to many of these questions. First there are three kinds of lead/acid batteries: 1- automobile batteries in which we include the big D8 diesel or tractors batteries; 2- marine batteries; 3- RV (recreational vehicle) or deep cycle batteries.

How to understand the difference between them

Automobile batteries (SLA) are known by everyone because we use them to start our car. They can develop a lot of energy even in cold weather. The discharge time is limited to about 10 minutes, especially if we do not succeed starting our automobile motor in cold weather (-25F). They have many thin lead plates that have a high rate of discharge to give the necessary energy to start the motor. They are not suitable for a long time use of a slow discharge rate like lighting or for an electric outboard motor. Marine batteries have the same construction as the car batteries except that their plates have their bottom taken or glued in epoxy to prevent brakeage when the boat is knocked by the waves or with the vibration. Also they are not suitable for lighting or for trolling motors.

Deep cycle batteries have their plates thicker and generally longer than the previous ones. This type of construction gives a longer and a slower rate of discharge necessary for lighting, the water pump or for the trolling motor. Very important here: if you do not see on the battery DEEP CYCLE OR RV, then it is not a deep cycle battery. These batteries are the only ones suitable for the good operation of electric trolling outboard motors. If you ever tried a standard car battery you certainly noticed that they were not suitable because it was discharging too fast, so you were not able to come back to the camp.

How to recharge them

A dual-purpose battery charger gives the same voltage for the car battery or for the deep cycle battery. Gasoline generators have generally an output of 12 volts for charging batteries but it is for car batteries and rarely gives more than 8.5 amp of charging rate. We can easily give a higher charging voltage to deep cycle batteries and a rate of charge of 12 to 20 amps is preferable. In such batteries we can easily give 15.5 volts because they have a hard head and need a higher voltage.

Most of the salesmen who sell batteries will tell you to completely discharge your batteries before recharging them. It is completely false and they are not manufacturers of batteries but salesmen. And with the words deep cycle we would be prone to think that it is true. If you proceed this way your batteries will not last more than 2 years.

A fully discharged battery should recharged as soon as possible to keep the activity in the battery. A battery that is completely dead for more than 12 hours begins to sulfate itself and shorten its life. After 24 hours there is one full year of life lost in the battery. If it happens many times during a season, you certainly have a very good battery if it still last one more year.

One example

Suppose that you go for fishing for a weekend with your new batteries and motor. Friday night you fish all evening. Then Saturday you completely discharge the battery and take the second battery and use it also on Saturday and discharge it completely and you have to paddle to go back to your cabin. When you are back to your house you store everything in your basement. Then Monday night you begin to charge the first battery until Wednesday and the other one for a couple of days. Which battery has been discharged first? OH OH, you do not remember because you bought them in the same time and they are identical. So maybe one or both batteries will have lost one year of life. So after 5 or 6 fishing trips, if you made the same, how old are your batteries? If you do not have any charging device at your cabin, you should use at least booster cables and charge them with your car to keep them in activity even if it is a slight charge. By proceeding this way you will at least prevent the batteries from sulfating. You can also use a wind generator and or a solar panel. A wind generator is preferable because most solar panels do not produce enough energy to give a quick charge to the batteries except if you are located in Florida “SUNSHINE STATE”. We must not forget that in winter the sunshine time is shorter than in summer and perhaps that you may have snow over the solar panel and possibly it is impossible to reach the cabin!

Necessary care of batteries

Carrying batteries from your house to the cabin is not always a pleasant job because they are heavy to manipulate. It is recommended to leave them where you will use them and use a charging device like a wind generator or a gasoline generator for emergency use. If you have a wind generator you can use it to recharge batteries while you sleep and light your cabin. Even if there is no wind, batteries have the possibility to transfer the charge from one battery to the other one for your trolling motor. Batteries connected in parallel are like U-tube… the mostly charged will empty itself in the less charged battery and equilibrate both at the same charge voltage after a few hours. A battery that is recharged immediately after its use will last at least 7 to 8 years if they are maintained this way. In winter if you bring back your batteries at home you should avoid to keep them on a concrete floor; you have to put them on a wood floor and give them a charge at least at every 4 to 6 weeks to keep them in activity.

It is also good to buy a hydrometer to check the gravity of the batteries. At 1275 the battery is fully charged. When the gravity is between 1100 to 1200 the battery is completely discharged or ready to send to the garbage. It is important to check all cells separately because it is possible that one is faulty and this time is the right time to change the battery. When many batteries are connected in parallel, just one faulty cell can drain all the batteries. So it is important to make check one in a while.

** The author of this article is the president of ELECTROVENT manufacturer of wind generators

located at 663 rue Routhier, Sainte-Foy, P.Q. G1X 3J8 Canada. You can see the products of ELECTROVENT (wind generators and Hydro Alternators for generating electricity in small stream) by visiting the website

Answers to the most common Frequently Asked Questions about batteries used in all applications.