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Trolling Motor Batteries - Lead Acid vs AGM vs Lithium LiFePO4 - Is Lithium Worth It?

Posted by Matt Pierce on

Trolling Motor Batteries Basics

Lead Acid vs AGM vs Lithium (LiFePO4)

 Video Presentation

Common Terms

DOD - Depth of discharge - % of battery used
SOC - State of charge - what % the battery is full
BMS - Battery Management System
AH - Amp Hours the amount of energy in your battery
Parallel - Batteries wired in parallel will increase the total AH but keep the voltage the same
Series - Batteries wired in series will increase the voltage but keep the same AH

Types of Batteries

Deep Cycle Lead Acid - Marine Grade


For trolling motor use you will want to look for a deep cycle battery. Deep cycle batteries are made to be slowly drained and recharged unlike a starting battery that is used for quick bursts of power.


Historically Lead Acid is the most common type of deep cycle battery.  With a high quality battery you can get about 2-3 yrs of use if properly maintained. 

Pros

  • Lowest cost

Cons

  • Requires maintenance - cells need to be topped off
  • May leak or spill
  • Subject to premature failure if discharged beyond 50% DOD
  • Weight (about 60 lbs for a group 31)
  • Limited 1 yr warranty

AGM (Absorbed Glass Mat) - Deep Cycle Marine Grade

 

Duracell Group 31 AGM Marine Battery

AGM batteries are also a lead acid battery but are completely sealed so they require no maintenance. You can also expect to get about 2-3 years of use with a high quality battery if properly maintained. 

Pros

  • Medium cost (about 1.5-2x of a basic lead acid)
  • Sealed - no maintenance required not subject to spills

Cons

  • Subject to premature failure if discharged beyond 50% DOD
  • Weight (about 60 lbs for a group 31)
  • Limited 1-1.5 yr warranty

Lithium - LiFePO4 (Lithium Iron Phosphate)

aolithium 12v 100aH Lithium LiFePO4 Battery

LiFePO4 Batteries are the latest in battery technology.  Lithium batteries have a higher upfront cost but many advantages that may help justify the additional expense. 

Pros

  • 10 Yr Life - 5-10+ Yr Warranty’s Available, 3-5000+ Cycle Count
  • Weight savings - 25lbs vs 60-70lbs
  • Longer Runtime - can be safely discharged to 90% DOD
  • Sealed - no maintenance required not subject to spills
  • BMS - Battery Managment System, Computer built-into the battery
  • Full voltage during discharge
  • Faster Charging - Due to the way LiFePO4 charges & capable of charging at higher AMPs

Cons

  • High Initial Cost
  • Special requirements for charging in cold weather (below 32F)

Lead Acid vs Lithium (LiFePO4) Discharge Rates

One of the advantages of Lithium is you get full voltage during the discharge of the battery as shown in the chart above.  With Lead Acid batteries the voltage drops as they are discharged.  Using Lead Acid I would consistently have to bump up the speed of my trolling motor as the batteries discharged to compensate for the voltage drop. 

Important Note: If you are using a trolling motor that automatically deploys and stows, like the Ulterra and using a Lithium battery, make sure you have a way to monitor your state of charge. As the battery gets to the end of its charge it will quickly go from full voltage to 0 which will prevent you from being able to auto stow your trolling motor.

 Lead Acid vs Lithium (LiFePO4) DOD Degradation

*LiFePO4 are rated to 3-5K cycles at 90% DOD

Lead Acid Battery Cycle service life

As shown on the chart above Lead Acid batteries lifespan is greatly reduced if you discharge more than 50%. With Lithium you can safely discharge to 90%+.  This effectively doubles the safe useable runtime of your batteries.  When I used Lead Acid, generally I would use my batteries as long as I could and ignored the 50% rule.  As a result I would only get 1 - 2 years out of the batteries before the runtime was greatly reduced.  This is one of the primary reasons I decided to switch to Lithium.

Battery Wiring Schematics 

Trolling Motor Runtime

Example based on my experience with Ulterra 112lb & 23ft Lund Boat.  Actual results may vary.

Runtime = Battery Amp Hr Rating / Trolling Motor Amp Draw 

Example:
36V 100 AH Batteries (3x 12V 100Ah Batteries wired in series)
112lb Thrust Trolling Motor (52 Max Amps)
Average of 35% power - Trolling 1.2mph (~level 4-5).  This was calculated based on the runtime I have been getting on a new set of batteries.

100AH / (52*35%) = ~5.5hr
50AH recommended usable with Lead Acid = 2.7hr
90AH usable with Lithium = 4.95hr

The chart below is data from Minn Kota that you can use to estimate the amp draw based on the motor you are using.

 

Onboard Charger & Charging

  • Amps per bank = Charge Rate
  • 10 Amp Charger will charge a empty 100 AH battery in about 10-12 hrs. Lithium is more efficient so charge times will be less than Lead Acid
  • Lead Acid can support 25% of capacity for charge rate (eg. 100 AH battery can be charged upto a 25 Amp Charger)
  • LiFePO4 can support 50% of capacity for charge rate (eg 100 AH battery can be charged unto a 50 Amp Charger)
  • Most manufactures recommend not regularly charging at the maximum charge rate.  The most common onboard multi-bank chargers range from 5-15 amps per bank.
  • I am currently using a NOCO Genius GENPRO10X3, 3-Bank, 30-Amp (10-Amp Per Bank)
  • Not all chargers support Lithium

 

What to look for in Lithium (LiFePO4) Batteries

  • BMS - Battery Management System
  • Bluetooth to monitor SOC (state of charge) very important if using Ulterra or other trolling motor that auto deploys / stows
  • Cold Weather Charging Protection - won't let the battery charge if below 32 degrees
  • Cold Weather Heater - if the battery is below 32 degrees it will heat the battery before charging
  • Sealed or Serviceable
  • Customer Service and Reviews
  • Compatible with Parallel or Series Systems
  • Warranty

Recommended Lithium LiFePO4 Options

 

The batteries below are some of the ones I put on my short list as I was deciding what lithium battery to go with.  I ultimately decided to go with the aolithium 12v 100Ah battery.  For my use case it gave me all the requirements I was looking for - Bluetooth BMS to be able to monitor the SOC from my phone so I could make sure to stow my Ulterra before my battery got too low, cold weather protection to prevent damage to the battery if the temperature was below 32 deg, 8 YR warranty.  I also messaged back and forth with aolithium and they were quick to respond and answer my questions.

 
Ampere Time 12v 100Ah CHINS 12V 100Ah Chins 12V 100Ah Smart Bluetooth aolithium 12V 100Ah Smart Bluetooth Battle Born 12V 100Ah Dakota Lithium 12V 100Ah
BMS Basic or Bluetooth Basic Basic Bluetooth Bluetooth  Basic Basic
Monitor SOC from App No No Yes Yes No

No
Cold Weather Protection No No Yes Yes Yes No
Cold Weather Heater No No Yes No No No
Sealed or Serviceable Sealed Sealed  Sealed  Serviceable  Sealed Sealed
Warranty 5 YR 3 YR 3 YR 8 YR 10 YR 11 YR
Cost* $399 $359 $499 $599 $879 $899

 

 

General Guidelines

  • Always use the same brand, size and age of battery(s) in a series or parallel setup
  • For trolling motor use use a battery that is marine rated or has a waterproof rating if Lithium
  • Use appropriate size wiring and fuses / breakers (not covered in this presentation)
  • Use an onboard charger and keep your batteries plugged in when not in use
  • If using lead acid make sure to regularly check and fill battery