My Deep Cycle Battery and Trolling Motor Info page
Here is what I have discovered concerning the use of the trolling motor and deep cycle battery. Please remember I am not a expert. This is what I have discovered from many different sources. Any of which may be wrong.
Many people complain that when using a trolling motor the battery does not last. This is caused by using a ordinary battery. A vehicle battery is designed to supply a large amount of power for a very short amount of time. A trolling motor requires a fair amount of power for a long time. Because of this a deep cycle battery is constructed to withstand being drained and recharged without damage.
You can tell the charge level of a deep cycle battery using a voltmeter or a hydrometer. I use a voltmeter. It is less precise but easier to use for a beginner. My battery is a Nautilus Gold Battery sold by Canadian Tire. Here is the table I found for this battery. I have been informed that every type of battery has its own voltage table and you should get it from the manufacturer, but here is the table for mine.
Never test a battery with a voltmeter under load. You will get a reading lower then the correct voltage. Turn off your motor and other accessories running under the battery before the test. You should also note that when a battery is drained quickly such as with a trolling motor the voltage will climb for about eight hours after the load is taken off the battery. You will have to wait that long for a accurate reading. Obviously if you are on the water and using voltage to determine the level of the battery waiting eight hours is a little impracticle. I take the reading as is. I don't get as much time out of a battery before I concider it discharged however, better safe then sorry.
12.6v - 100%
12.4v - 75%
12.2v - 50%
12.0v - 25%
11.8v - 0%
You may wonder why the voltage for 0% is so high. That is because you should never drain a deep cycle battery below 70% of the total capacity. When you reach 11.8v you are at that 70% mark of total capacity and should stop using the battery. Going past this point shortens the life of the battery.
When recharging do yourself a favour and get a automatic charger for deep cycle batteries. I thought that recharging my battery would be easy, but it is a pain. You need to charge the battery up to full capacity, but there is a catch. The voltage will drop for 24 hrs after charging. This is normal, but causes problems if you are using voltage to tell how much of a charge to put in the battery. A automatic charger for deep cycle batteries will slowly charge you battery, and will reduce that amperage being put into the battery as it gets closer to finishing. This seems to help with the voltage drop problem and reduces the chances of the battery being overcharged. Also it will cut out when the battery is charged and will top it off again as the voltage drops. Canadian Tire sells a Nautilus Charger Especially for the Nautilus Batteries. That is what I have.
Battery Sulfurization and Solar Panels - When a battery is partially or completely discharged sulphur builds on the metal plates inside. If this partiall discharged battery is not still being discharged or charged, but is just sitting there the sulphur will begin to harden making recharging the battery back to its original state more difficult. This is sulfurization and it is the leading cause of premature failure of a battery. In motor boats where the battery is continually either being charged, discharged, or is fully charged sulphuization is not as much of a problem as it is in a sail boat where if a battery is partially discharged it is necessary to wait until you return to home where you can recharge it. However permanent sulphuization supposedly will not occur if the battery is under even a tiny charge. Therefore you should be able to avoid sulphurization in a sail boat with just a small solar panel. Personnally I like to have at least a 15 watt panel for each battery to ensure I get at least some power going to the batteries under most conditions. However this is just a personal choice.
RANGE EXTENDERS-Have you ever wondered about those range extenders that are supposed to greatly increase the range of a trolling motor and wondered what they did. Here is what I have found out. It seems the less expensive motors control engine speed by using a resisting coil, which converts electricity to heat. It is located in the part of the engine that is in the water and the heat is dissipated there. The disadvantage is that this system is highly inefficient. Going from full power to half power does not save near as much energy as it should because this system is so inefficient. A more expensive engine or one with the range extender quickly turns the power on and off to regulate speed. So if you are at half power the engine quickly turns the power on and off so that the power is only on half of the time. The greatly extends the range of the engine. I have heard it can extend running time from 5 to 8 times. However the external range extender seem to be impossible to find. I would like to get one for my boat, but have been unable to find one.