Quick Answer
How long a 12v battery will run a trolling motor depends on several factors:
– Battery capacity – Measured in amp hours (Ah), higher capacity batteries will run longer. A typical deep cycle battery for trolling motors is around 100Ah.
– Motor thrust – Higher thrust motors will draw more current and drain the battery faster. Trolling motors are typically 30-80 lbs thrust.
– Speed setting – Running the motor on higher speeds will draw more power and drain the battery faster. Most motors have 5 speed settings.
– Overall efficiency – Factors like motor condition, prop condition, and water conditions impact power efficiency.
As a general estimate, a 100Ah deep cycle battery should run a common 55 lb thrust trolling motor on medium speed for about 5-8 hours. Larger batteries around 120-150Ah would run closer to 10 hours.
Battery Capacity
Battery capacity is one of the most important factors in determining trolling motor runtime. Capacity is measured in amp hours (Ah). An amp hour represents the amount of current (amps) that can be drawn from the battery over the course of 1 hour, until the voltage drops below a usable level.
For example, a 100Ah battery could theoretically deliver 1 amp for 100 hours, 2 amps for 50 hours, or 10 amps for 10 hours. Of course in real world conditions it’s more complicated, but this gives a basic idea of capacity.
Deep cycle lead acid and lithium batteries designed for trolling motors typically range from around 70Ah to 150Ah. The most common size is a 100Ah battery, which provides a good balance of power versus weight and cost.
As a very rough estimate, a 100Ah battery will operate a typical 55lb thrust trolling motor for 5-10 hours, depending on other factors. A 70Ah battery might only last 3-6 hours, while a 120-150Ah battery could potentially run 10-15 hours.
When selecting a battery, choose the largest capacity that is practical for your boat setup and budget. This will allow you to stay on the water longer between charges.
| Battery Capacity | Estimated Run Time |
|---|---|
| 70Ah | 3-6 hours |
| 100Ah (typical size) | 5-10 hours |
| 120-150Ah | 10-15 hours |
Motor Thrust
The thrust rating of the trolling motor also greatly impacts battery runtime. Thrust is a measure of power, rated in pounds of force. Most common trolling motors designed for 12-24v systems are in the 30 to 80 pound thrust range.
Higher poundage equals more power draw and faster battery drain. A 30lb thrust motor will run significantly longer than an 80lb thrust on the same battery.
However, higher thrust allows you to run at faster speeds and maneuver larger boats, so you need to balance run time versus power.
For medium sized boats (16-20ft), a 55lb thrust motor is common. On a typical 100Ah battery, this motor would run for around 5-8 hours at a moderate speed.
Going up to a 70lb thrust motor may decrease run time by 1-2 hours. Dropping down to a 45lb thrust could potentially add 1-2 hours.
| Motor Thrust | Run Time (est.) |
|---|---|
| 30lb | 7-10 hours |
| 45lb | 6-9 hours |
| 55lb (typical) | 5-8 hours |
| 70lb | 4-6 hours |
| 80lb | 3-5 hours |
Speed Setting
Most trolling motors have variable speed settings, usually 5 speeds from very slow to full power. Running at slower speeds puts less load on the motor and conserves battery capacity.
For example, you might be able to run a motor for 8 hours at a medium cruising speed, but only 5 hours at full throttle.
Whenever possible use the lower speed settings to extend your battery life. Only increase speed when needed for maneuvering or fighting currents or wind.
Here is a table estimating run times on a typical 100Ah battery and 55lb thrust motor at different speed settings:
| Speed Setting | Run Time (est.) |
|---|---|
| 1 – Slowest | 9-12 hours |
| 2 – Slower | 7-10 hours |
| 3 – Moderate Cruise | 5-8 hours |
| 4 – Faster | 4-6 hours |
| 5 – Full Throttle | 3-5 hours |
Efficiency
A few other factors impact the overall efficiency and battery drainage of your trolling setup:
– Motor condition – Old worn brushes and bearings decrease efficiency
– Prop condition – Damaged and unbalanced props require more power
– Water conditions – Fighting wind, waves, and currents draws more power
– Boat loading – Heavy loads require more thrust and power
– Maintenance – Keep battery terminals clean, lubricated, and secure
– Temperature – Colder temperatures degrade lead acid battery capacity
Optimizing these factors where possible will maximize your runtime. Having your lower unit serviced regularly and choosing the right prop for your boat helps. Avoid rough water and adverse winds when feasible.
In ideal conditions you can achieve the higher range estimates. Under less optimal real world conditions your run times may be a bit lower.
Maximizing Run Time
Here are a few key tips to get the most running time from your trolling battery:
– Choose the largest battery capacity you can
– Use lower thrust motors when practical
– Use the slower speed settings as much as feasible
– Maintain your motor lower unit and prop
– Fish in favorable conditions when possible
– Charge battery fully before each trip
– Consider lithium batteries for increased capacity
Conclusion
Estimating electric trolling motor run time depends on several interrelated factors, but the battery capacity and motor thrust are the most critical determinants.
As a general guideline, a typical 100Ah deep cycle battery paired with a 55lb thrust trolling motor will run for 5-8 hours at moderate cruising speed. Larger batteries around 120-150Ah could potentially run for 10-15 hours under optimum conditions.
To maximize your runtime, choose an appropriately sized battery, match it with an suitable motor, use lower speed settings when feasible, and maintain your equipment properly. Understanding these key factors will help ensure you can operate all day on the water without running out of battery capacity.
With lithium battery technology continuing to improve, runtimes will only increase in the future. But for now, you can still achieve excellent runtimes with today’s deep cycle lead acid batteries if properly matched to your motor and boating application.