Lithium Trolling Motor Batteries
Few years ago, lithium batteries were considered as something exotic, futuristic, but with the improvements in technology, lithium batteries more and more present in our everyday lives. Lithium trolling motor batteries initially cost several times more than the AGM SLA batteries of the same capacity, but they can save significant amount of weight and can outlast AGM batteries 5-10 times.
These are the reasons why lithium batteries are becoming more and more popular as lightweight but long lasting deep cycle trolling motor batteries.
Trolling Motors - Features and Specifications
Electric trolling motors are used when quiet, simple and efficient propulsion is required. Main power sources are onboard batteries that supply required current at rated voltage. Most smaller electric trolling motors operate at 12 volts, but other voltages are used as well:
- 12 V are used for a thrust up to a 60-65 pounds,
- 24 V are used for a thrust up to a 100 pounds,
- 36 V are used for motors that provide more than 100 pounds of thrust.
By increasing the operating voltage, maximum currents are kept under 50-60 Amps, which is very important for keeping the cables not too thick.
Following table lists the most popular electric trolling motors:
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During operation, electric trolling motors are not constantly pushed at the maximum - they must have certain power reserve in order to be able to push the boat in the emergencies.
But, just like electric trolling motors, trolling motor batteries must be dimensioned to include certain power reserve, in order to be able to power accompanying motors in emergencies as well.
So, when calculating required battery capacity, it is recommended to always use maximum motor current - and even then add some reserve, just in case.
Little bit of math: If you have Newport Vessels 62lb Thrust NV-Series electric trolling motor with maximum current of 58 Amps at 12 volts and you want to have autonomy of at least two hours, your battery must have 2h capacity of ~120 Ah.
Since the capacity of the batteries is value measured when the battery is being discharged with constant current for 20h, actual 2h capacity is lesser than 20h capacity, especially for AGM SLA batteries.
- 20h capacity of 104 Ah,
- 2h capacity of 'only' 62 Ah.
Note: these values are measured at 77°F (25°C), for the new, fully charged battery being discharged down to 10.5 volts (1.75 volts per cell).
In order to be able to power Newport Vessels 62lb Thrust NV-Series for two hours at full throttle, one must connect two UPG UB121000 batteries in parallel for effective 122 Ah capacity when the batteries are discharged for 2 hours!
Of course, this also doubles the weight of the battery pack from 64 pounds (29 kg) to 128 pounds (58 kg) - and that is rather heavy just to carry around :)
And that is where lithium trolling motor batteries come to play!
For more about this topic, feel free to check out Electric Trolling Motors for Small Boats, Pontoons, Kayaks and Canoes article.
Rechargeable Lithium Batteries - IMR, INR, IFR, and ICR Lithium Batteries
There are numerous potential lithium ion battery chemistries, but most common are sometimes 'hidden' via abbreviations like IMR, INR, IFR, or ICR. These abbreviations describe actual battery chemistry:
- IMR lithium ion batteries feature LiMn204 (Lithium Manganese Oxide) chemistry. Their nominal voltage is 3.6 - 3.7 V per cell, with the maximum recommended charging voltage of 4.2 V per cell. IMR batteries commonly have smaller capacity, but are capable of delivering large currents and are often used in the starting lithium ion batteries.
- INR lithium ion batteries feature LiNiMnCoO2 (Lithium Manganese Nickel) chemistry. These batteries are very similar to IMR batteries, since they can provide plenty of currents, with slightly lower capacity. INR lithium ion batteries are commonly used in starting and power tools batteries.
- IFR lithium ion batteries feature LiFePO4 (Lithium Iron Phosphate) chemistry. Their nominal voltage is 3.2 - 3.3 V per cell, with the maximum recommended charging voltage of 3.5 - 3.6 V. They can't provide extra large currents, but are much safer than other lithium ion batteries and are commonly used as 'drop-in' replacements with some sort of Battery Management System (BMS) in place.
- ICR lithium ion batteries feature LiCoO2 (Lithium Cobalt Oxide) chemistry. Their nominal voltage is 3.6 - 3.7 V per cell, with the maximum recommended charging voltage of 4.2 V. They commonly have higher capacities, but maximum allowed currents are often limited to just few C. ICR lithium ion batteries are used for low-current, deep cycle applications.
Note: there are other lithium battery chemistries on the market too, like: Lithium Nickel Cobalt Oxide (LiNiCoO2), Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2), etc. These hybrid technologies often feature improved charging/discharging features with improved safety, but the cost of such batteries is still too high for everyday use.
Commonly, lithium electric trolling motor batteries are 'IFR lithium ion batteries', featuring LiFePO4 (Lithium Iron Phosphate) chemistry. They are the safest for use and with proper BMS they can safely replace AGM SLA batteries in most applications - trolling motor batteries included.
Advantages of Lithium Trolling Motor Batteries
The main disadvantage of the lithium trolling motor batteries is their initial price, which is easily 3-4 times the price of the equivalent AGM SLA battery of the same capacity.
But, lithium trolling motor batteries advantages include:
- larger number of charging/discharging cycles. While deep cycle AGM batteries can withstand 400-500 cycles (at most) when being discharged down to 80% DoD (Depth of Discharge) or 20% of SoC (State of Charge), many lithium ion LiFePO4 batteries with the proper BMS can withstand at least 2000 charging/discharging cycles commonly down to 100% of DoD (when BMS cuts off the battery), with some high-end models easily tolerating 5000 cycles down to 80% and even 100% DoD.
- output voltage of lithium batteries is much more stable during operation, although this depends on the built-in BSM and rest of electronics.
- lithium batteries are 2.5-3 times, sometimes even more lighter than their AGM equivalents, saving plenty of weight.
- lithium batteries feature very low self discharge values and can be stored for months (6-12 months) with the minimal loss of charge.
- lesser drop of capacity when being discharged with slightly higher currents.
Other issues of the rechargeable lithium batteries are:
- safety concerns: most lithium trolling motor batteries are Lithium Iron Phosphate batteries which are relatively safe to use. When combined with BMS, they are safe to use since BMS systems monitor condition of the individual battery cells and the whole battery pack and act accordingly.
- connecting in parallel: lithium trolling batteries can be connected in parallel only if their BMS are intended for such use.
- lithium battery charging: lithium trolling batteries can be charged with intelligent AGM battery chargers or onboard alternators if their BMS systems are built for such charging - practically all 'drop-in' replacement batteries do feature such BMS systems, but it is recommended to check prior ordering.
Examples of Lithium Trolling Motor Batteries
The following table lists some of the most popular lithium trolling motor batteries:
|Model||Battery Type||Goup Size||Cell Type||20h Capacity (Ah)||CCA||MCA||RC||Weight (lbs/kg)|
|AIMS Power LFP12V100A||Deep Cycle||-||LiFePO4||100||-||-||-||30.2 lbs; 13.7 kg|
|Battle Born 100Ah 12V LiFePO4 Battery||Deep Cycle||31||LiFePO4||100||-||-||-||29 lbs; 13.2 kg|
|Eastup 1250750||Dual Purpose||-||LiFePO4||50||750||930||-||15.43 lbs; ~7.0 kg|
|GreenLiFE GL260-260AH||Deep Cycle||8D||LiFePO4||260||-||-||620 min||80 lbs; 36.24 kg|
|GreenLiFE GL80-80AH||Deep Cycle||27||LiFePO4||80||-||-||190 min||28 lbs; 12.8 kg|
|Mighty Max ML100-12Li||Deep Cycle||30H||LiFePO4||100||-||-||-||29.54 lbs; 13.4 kg|
|Renogy 12 Volt 50Ah||Deep Cycle||-||LiFePO4||50||-||-||-||14.77 lbs; 6.7 kg|
|Renogy 12 Volt 100Ah||Deep Cycle||-||LiFePO4||100||-||-||-||28.1 lbs; 12.73 kg|
|Renogy 12 Volt 170Ah||Deep Cycle||-||LiFePO4||170||-||-||-||46.3 lbs; 20.97 kg|
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As one can see, these batteries are much lighter than AGM SLA batteries.
Also, capacity drop is not as nearly as capacity drop in AGM SLA batteries, and when not discharged with strong currents, there is practically no capacity drop.
For example, GreenLiFE GL260-260AH features:
- 260 Ah 20h capacity (13 Amps for 20 h),
- 260 Ah 13h capacity (20 Amps for 13 hours),
- 260 Ah 5h 12 min capacity (50 Amps for 5h and 12 minutes).
So, no capacity loss for currents up to 50 Amps - that means that this 80 lbs battery is able to power 50 Amps load for slightly more than 5 hours. Equivalent AGM battery (or battery pack) would weigh at least 170 or even more pounds, not to mention maximum number of charging/discharging cycles.
Long Story Short: Lithium trolling batteries are not part of Science Fiction any more. They do cost more, initially, but in the long run, they save money and if the batteries must be carried regularly, they also save plenty of effort :)
Also, these batteries are commonly used in off-the-grid applications, as RV house batteries, solar batteries, golf cart batteries, various electric vehicles etc.
Before ordering new trolling motor battery, consider lithium batteries as well, just be sure that they feature good BMS systems that in combination with battery features (dimensions, capacity, maximum current), fit your needs and requirements.
Don't forget - safety first!