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How to Choose a Marine Battery for Your Trolling Motor

Choosing the perfect marine battery for your electric trolling motor is very much important. Because it’s the main solution in trolling power. How will be fishing or boating experience on the water it depends the right solution of electric power. So we should know exactly what is the method to choosing best marine batteries.

The first step in selecting a battery is to carry out an energy balance that allows evaluating the daily power consumption needs.

The result of this assessment as well as taking into account equipment that requires high power (starter, windlass) will make it possible to choose a suitable battery.

Points to consider when choosing a battery are:

  • Technology
  • ​The capacity sizing and impact on service life.
  • ​Lifespan and a number of cycles.
  • ​The maximum intensity
  • ​The dimensions
  • The weight
  • Conclusion

Technology:

In general, two batteries will be installed for safety reasons, one for starting the electric motor and the other for servitude.

Marine use requires both a battery capable of accepting deep discharges and a great maximum intensity for the operation of the windlass for example. The announced performance must be consistent with the battery technology.

Capacity sizing and impact on park life

The capacity is expressed in Amperes hour, usable for a given period; it corresponds to an amount of energy available for a particular time. If there is no precision, the capacity corresponds to a consumption over 20 hours.

This notion of duration is denoted Ct where t corresponds to the period. For example, for a 100 Ah C20 battery, 5 A per hour for 20 h may be used, ie a total of 100 Ah but only 8 A for 10 h, ie 80 A and 10 A for 5 h, ie 50 A. The capacity of the battery decreases so much faster as the discharge intensity is high

Nevertheless, in order not to damage a marine battery, it is not necessary to exceed the permissible discharge limits according to the technology (up to 80% for an AGM or Gel see table above).

For a typical marine use, it will be considered that the trolling motor battery is recharged once a day (with a charger for example) and that therefore the C20 value is a good indicator.

To choose the capacity, from the moment the marine batteries accept discharges up to 80% (case of gels or AGM batteries), one can consider two methods.

1) Calculation with a discharge of 50%. The main advantage is that the number of cycles is increased substantially and thus the cost per cycle is decreased. The marine battery pack will have a longer service life. This also makes it possible to maintain a margin of safety.

2) Calculation with an 80% discharge. The cost is greater but the bulk of the marine batteries is reduced by 37%.

2) Calculation with an 80% discharge. The cost is much, but 37% reduces the bulk of the marine batteries.

For 50% discharges AGM batteries are the most advantageous. If one takes into account in addition, the lower purchase cost and the fact that they are able to accept higher charge / discharge intensities than gel batteries, they are very well adapted to trolling motor use.

The gel batteries prove to be less expensive for deep discharges and have the advantage of being able to be left unloaded at 100% without damage.

Lifetime and number of cycles:

Type Number of cycles for a 75% discharge Number of cycles for a 50% discharge Life in a years at 20 ° C (permanent load) Self-discharge per month

Liquid 150 350 6 6%

AGM 275 450 12 3%

Gel 420 650 12 2%

The maximum intensity:

To determine the maximum intensity required, read the intensity values ​​of the starter and the windlass, which are the two devices requiring the most power.

It is safer to dedicate a marine battery for starting which will constantly be charged (the energy consumed is immediately restored by the alternator) to always be able to start the trolling motor.

For the windlass we note the following points:

It does not consume much energy, if you take the case of an 800 watt windlass, it will typically consume 85 amp in lifting. If it is used for 4 min this will correspond to a power consumption of 6 Ah.

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The necessary power is important, which will need to dimension the cables correctly, especially when the distance from the windlass to the trolling motor battery is high. For more information, see the wiring chapter.

The maximum intensity is high and necessary for a relatively long period.

The most suitable mounting is to connect the windlass to the starter battery and use the engine on. This is in fact always sufficiently recharged, which is not necessarily the case of the battery of servitude after a prolonged stay on an anchorage. On the other hand, the energy required for the windlass will be restored quickly to the starter marine battery thanks to the alternator.

Conclusion:

The service of the trolling motor battery will not withstand high discharge intensities. However, for safety reasons it may be advantageous to set up a system for using the service of the battery to start the trolling motor in the event of a starter battery failure. In this case, it must be confirmed that the service battery can supply power to the starter. Often this will often be the case, as the battery pack has a large capacity to deliver the starting current.

The dimensions:

The capacity of coverage larger electric motor (Ex. 24 volt trolling motor batteries) batteries dimensions.

Examples of dimensions:

Capacity Length Width Height

75 A / h 242 mm , 175 mm 190 mm

105 A / h 330 mm 175 mm 240 mm

200 A / h 520 mm 230 mm 240 mm

A marine battery should be placed as cool and ventilated as possible.

Depending on the space available on the boat, it will be necessary to either buy a large battery or buy two small batteries.

The weight:

This point is also important because the greater the need for capacity, the greater the weight will be. Some boats have a capacity requirement that can exceed 800 Ah, which involves more than 250 kg of battery. Ensure that the installation is optimized (charging system and correct wiring sizing ...) before installing such battery pack.

To set the ideas, here are examples of battery weights:

Capacity Weight

75 A / h 22 kg

100 A / h 30 kg

200 A / h 66 kg

To facilitate handling, it may be necessary to install two batteries in parallel rather than one with a larger capacity. As far as possible, it is better to put a single battery, but the installation of the marine batteries in parallel poses no problem from the moment when they are similarly old and the same technology.

Conclusion:

This page shows that limiting the depth of discharge requires the use of larger capacity (24 or 36 volts) marine or trolling motor batteries but that the cost is reduced in the medium term by a gain in longevity (with the exception of the gel battery). This also makes it possible to provide a safe margin of energy. Various criteria can be taken into account such as weight or congestion in the case of regatta use. In this case the choice will be inverse using the maximum performance of the marine battery to limit the capacity, therefore the weight of the battery.

Regarding technology, AGM batteries have the most interesting characteristics, they are more efficient than conventional cells and are more profitable if one refers to the price per number of cycles. If one takes into account the oversizing necessary to have an equivalent number of cycles with liquid batteries, AGM batteries will be more economical including in installation prices. As for gelled batteries, their performances are superior and they have the advantage of being able to be used even in turned-up position.

It should also be pointed that the lifetime of the battery depends largely on the quality of the charge cycle and that it is important to optimize it.

Numerous other parameters must be taken into account when determining the quality of a marine battery. The above data are typical of what is generally observed. However, it may well be that an AGM battery from manufacturer A has better performance than the manufacturer's gel battery. For this reason, it is necessary to first rely on the performance data supplied with the battery. At last we hope, if you consider these data and others matter (Confused choosing one? Here is a good list by TrollingPowerSolution.com), you most able to pick your best trolling motor battery.

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