Choosing the right battery size for a trolling motor is confusing for one simple reason: people mix up voltage, amp-hours, and thrust as if they mean the same thing. They don’t.
This guide breaks the decision into a practical sequence you can actually use:
- Confirm your system voltage: 12V, 24V, or 36V
- Estimate current draw (amps) from how you fish, not just thrust
- Convert that into the battery capacity you need (Ah or Wh)
- Make sure the pack physically fits and the wiring is sized correctly
If you’re sourcing LiFePO4 packs for private label, OEM, or your own marine brand, this approach also helps you specify the pack clearly when you request a quote.
What battery size really means for a trolling motor
“Battery size” usually gets used in three different ways:
- Voltage: 12V, 24V, or 36V systems (how your motor is powered)
- Energy capacity: how much energy you can store (Ah or Wh)
- Physical size: whether it fits your tray (Group 24, Group 27, Group 31, custom case)
If you only match one of these, you can still end up disappointed. For example: a physically large battery that’s the wrong voltage won’t run the motor at all; a correct-voltage battery with too little energy will run—but not long enough.
How do you choose 12V, 24V, or 36V for trolling motor systems
Voltage is not a “bigger is always better” choice—it’s a system choice. Higher voltage typically allows the motor to deliver the same power with less current, which can reduce stress on wiring and improve efficiency.
Here’s a simple planning table anglers commonly use as a starting point (always confirm your motor’s requirement first):
| System voltage | Typical use case | Common thrust range you’ll see | What it usually improves |
|---|---|---|---|
| 12V | Smaller boats, lighter loads, shorter runs | Often up to about mid-range thrust classes | Simplicity, fewer batteries |
| 24V | Heavier boats, more wind/current, longer days | Mid to higher thrust classes | Better efficiency, more control under load |
| 36V | High-demand setups, big boats, strong current | High thrust classes | Strongest “hold position” feel and sustained performance |
Reality check: voltage does not replace capacity. A 24V system still needs enough total energy to last your day—it just changes how that energy is delivered.
Why thrust alone does not tell you the battery you need
Thrust is a mechanical output rating. Your battery planning needs an electrical input number: amps.
Two motors with similar thrust can pull different current depending on design, prop efficiency, and conditions. Wind, current, weeds, hull shape, and how often you use high throttle can easily dominate the real-world draw.
So instead of planning from thrust alone, plan from average current.
A practical approach:
- Find your motor’s max current draw from the spec sheet (or manufacturer data).
- Estimate your average draw based on how you actually fish:
- “Mostly low and medium throttle” is often far below max draw
- “Fighting wind all day” can push average much closer to peak
How to calculate trolling motor battery size and runtime
You can size by Ah (simpler) or Wh (more accurate across voltages). Use whichever is easier for your team.
Method 1: Simple Ah planning
Runtime in hours ≈ Usable Ah ÷ Average amps
For conservative planning with LiFePO4 packs, many users plan around about 80 percent usable of nameplate capacity in real conditions (not because lithium can’t go deeper, but because it builds margin for wind, aging, temperature, and surprise loads).
Example:
- 12V 100Ah pack
- Plan usable ≈ 80Ah
- If your average draw is 20A: runtime ≈ 80 ÷ 20 = 4 hours
Method 2: Wh planning for 12V vs 24V vs 36V comparisons
Energy in Wh = Voltage × Ah
Runtime in hours ≈ Usable Wh ÷ Average watts
Watts are amps × volts, so this method stays consistent when you compare different system voltages.
How many amp-hours do you need for real fishing days
Below is a practical runtime calculator style table you can use for quick planning. The “usable” column uses conservative assumptions so you don’t under-size.
Assumption for planning: usable capacity ≈ 80Ah from a 100Ah pack
| Average draw | Usable capacity | Estimated runtime |
|---|---|---|
| 10A | 80Ah | 8.0 hours |
| 15A | 80Ah | 5.3 hours |
| 20A | 80Ah | 4.0 hours |
| 30A | 80Ah | 2.7 hours |
| 40A | 80Ah | 2.0 hours |
If you fish a lot in wind or current, plan using a higher average draw than you “hope” you’ll see. Under-sizing is the most common reason customers feel lithium “didn’t meet expectations.”
Battery size chart for trolling motor setups using energy, not guesswork
When buyers ask for a “battery size chart,” what they usually want is a fast mapping between voltage choice and a reasonable starting capacity. Here’s a planning chart that keeps the logic consistent:
| System voltage | Typical pack configurations | A practical starting point for many users |
|---|---|---|
| 12V | 12V 100Ah, 12V 120Ah | Good starting point if your average draw is moderate |
| 24V | 24V 50Ah, 24V 100Ah | Better for higher demand; energy scales with Ah |
| 36V | 36V 50Ah, 36V 60Ah, 36V 100Ah | Often chosen for high-demand control and holding power |
Key idea: A “24V 50Ah” pack and a “12V 100Ah” pack store similar energy on paper (because volts × Ah), but they behave differently in current and wiring. Choose voltage based on your motor and use-case, then size energy based on runtime needs.
What about Group 24, Group 27, and Group 31 battery size
Group numbers are physical footprint standards, not performance ratings.
People commonly search “Group 24 vs Group 27 vs Group 31 for trolling motors” because lead-acid batteries are sold that way. With LiFePO4, you can often fit more usable energy into the same footprint because lithium has higher energy density and maintains voltage better under load. For procurement, this matters in two ways:
- You can keep a familiar footprint to simplify retrofits
- Or you can switch to a custom case if your tray or compartment is unusual
If you’re replacing lead-acid, confirm:
- Tray length, width, height clearance
- Terminal location and cable reach
- Hold-down method and vibration support
How do you avoid voltage sag and wiring losses
Many “battery feels weak” complaints are not battery capacity problems—they’re system loss problems. A few field-proven checks:
- Undersized cables cause voltage drop and wasted power as heat
- Loose lugs create resistance and intermittent cutoffs
- Incorrect fusing or breaker selection causes nuisance trips
- Overly long runs to the bow increase losses
If your motor draws high current at peak, cable selection and connection quality matter almost as much as battery capacity.
Why LiFePO4 often feels like an upgrade even at the same rated capacity
Two real-world differences many users notice quickly:
- Flatter voltage curve: performance feels more consistent late in the day
- Higher usable energy under load: lead-acid can feel sluggish as voltage sags
That’s why many anglers report that moving to LiFePO4 feels like a “power upgrade,” even when the label capacity looks similar.
When should you size up beyond your first estimate
If any of the following are true, you should plan extra energy margin:
- You fish in strong wind or current regularly
- Your boat is heavy, or you carry multiple anglers and gear
- You use high thrust for long periods rather than short bursts
- You run additional loads from the same bank
- You want multi-day use without recharging
A safe procurement habit is to size so your typical day uses only a comfortable portion of capacity. It reduces stress on the system and increases customer satisfaction.
What specifications should a buyer request from a LiFePO4 supplier
If you’re buying as a brand, distributor, or OEM customer, the battery “size” is only one line item. To avoid mismatch, request these specs:
- System voltage and configuration: 12V, 24V, 36V
- Capacity: Ah and calculated Wh
- Continuous discharge current and peak discharge current
- BMS protections: over-current, short-circuit, low-temp charge protection
- Charging recommendations: charger profile targets and limits
- Mechanical: dimensions, weight, terminals, case rating if needed
- Labeling and compliance documents for your market
- OEM and ODM support: branding, packaging, and documentation
This is where a supplier acts like a partner, not just a seller—because correct matching prevents the “it trips sometimes” and “it didn’t last as long as I expected” issues that lead to returns.
Ready to size a trolling motor battery pack for your boat
SAFTEC ENERGY supplies 12V LiFePO4 batteries and custom battery pack solutions for marine and off-grid applications. If you want a realistic sizing recommendation, send:
- Your trolling motor brand and model
- System voltage requirement
- Typical throttle usage and conditions
- Any additional loads on the same battery bank
- Available installation space and terminal preference
We’ll convert that into a practical pack recommendation and a quote, with OEM and ODM options available.
FAQ
Are lithium batteries worth it for a trolling motor
Often yes—if you fish regularly, lithium can win on total ownership cost and on-water consistency, not just weight.
A practical comparison is cost per usable cycle:
- Lead-acid typically loses “usable performance” sooner when cycled deep and when voltage sag becomes noticeable.
- LiFePO4 usually holds voltage better under load, so the motor feels more consistent late in the day.
If your current setup feels strong in the morning but weak in the afternoon, lithium’s flatter voltage behavior is often the biggest “real-world upgrade.”
Is a 100Ah lithium battery enough for a trolling motor
It can be—but the correct way to answer is based on system voltage and your average amp draw, not Ah alone.
Quick sizing method:
- Estimate your average draw (amps) based on your normal throttle usage and conditions
- Use a conservative usable capacity target (many anglers plan around 80Ah usable from a 100Ah pack for real-world margin)
- Runtime ≈ usable Ah ÷ average amps
If you share your trolling motor model and how you typically run it (light cruise vs heavy wind/current), we can give a realistic capacity recommendation rather than a generic guess.
How long will a 100Ah battery last with a 40 lb thrust trolling motor
Thrust is not the same as current draw, but you can still estimate reliably:
- Find the motor’s amp draw at the throttle you use most (spec sheet is best)
- Use: runtime ≈ usable Ah ÷ average amps
Example planning (for understanding):
- If average draw is ~20A and you plan ~80Ah usable, runtime ≈ 4 hours
- If you run near full throttle and average draw is ~40A, runtime ≈ 2 hours
Most real fishing time is longer than “full throttle math” because average current is usually lower than peak.
How long will a 100Ah battery last with a 55 lb thrust trolling motor
Same calculation—55 lb thrust setups often pull higher current under load, so full-throttle runtime is typically shorter.
The accurate answer depends on:
- your motor’s rated current curve (or max draw)
- wind/current and how aggressively you use higher speed settings
- boat weight and hull drag
If you tell us the motor brand/model, we can estimate using rated current instead of thrust-only assumptions.
What is the 80/20 rule for lithium batteries
It’s a common longevity habit: try to operate roughly between 20% and 80% state of charge for routine use.
Important clarifications:
- It’s not a “hard rule.” LiFePO4 can be used deeper when needed.
- The benefit is reduced stress over time, especially if you cycle frequently.
- For trolling motors, the practical version is simply: don’t size so tight that you must run near empty every trip.
Why are lithium batteries sometimes “not recommended” for trolling motors
Most warnings come from system mismatch, not the LiFePO4 chemistry itself. The top real-world causes are:
- Charging below freezing without low-temperature charge protection
- Using a charger profile designed for lead-acid (incorrect setpoints/behavior)
- Alternator charging without current limiting (can stress regulators)
- Underestimating peak current so the BMS trips under load
- Poor cable sizing or loose connections causing voltage drop and cutoffs
When the battery, BMS, cabling, and charging method are matched correctly, LiFePO4 is widely used for trolling applications.
Can I use a standard lead-acid charger for a lithium trolling motor battery
Only if the charger has a LiFePO4 mode or adjustable settings that match LiFePO4 charging requirements.
Why this matters:
- Many lead-acid chargers rely on long “float” behavior that isn’t needed for LiFePO4
- Some chargers can misread a BMS disconnect and behave unpredictably
- Undercharging is common when the profile is not lithium-correct
If you send the charger model number, we can tell you whether it’s compatible and what settings to use.
Will my outboard alternator charge a lithium battery
Sometimes—but it depends on alternator/regulator design and how the lithium bank accepts current.
Best-practice approach for many boats:
- Use a DC-DC charger between the alternator source and the LiFePO4 battery bank
- It limits current and applies a stable lithium charging profile
- It also reduces the risk of sustained high current draw that can stress some regulators
If you share your outboard model and your charging layout, we can recommend a safe charging path.
Can a lithium battery catch fire when not in use
LiFePO4 is considered one of the more thermally stable lithium chemistries, and well-built packs include BMS protections. Most storage incidents (across battery types) are tied to:
- physical damage
- incorrect charging equipment
- low-quality packs without robust protection
- parasitic loads or wiring faults
Practical storage checklist:
- store around mid state-of-charge for long storage periods
- disconnect parasitic loads
- keep the pack dry, secured, and away from impact
Tell us your storage duration and temperature range, and we can suggest a simple storage plan.
What size battery is best for a trolling motor: Group 24, 27, or 31
Group numbers describe physical size, not performance.
A better way to decide:
- Confirm the tray space you have (length, width, height clearance)
- Decide the system voltage (12V/24V/36V) your motor requires
- Size energy for your target runtime (Ah or Wh)
If you’re replacing lead-acid with LiFePO4, you can often get more usable performance in the same footprint—so “Group size” alone isn’t the deciding factor anymore.