The Monster Marine Lithium "Scorpion" (MML-13C120B) is a 12V 120Ah dual-purpose Bluetooth lithium iron phosphate (LiFePO₄) cranking battery rated at 1300 cold cranking amps, built in a Group 31 case for starting and deep-cycle use on marine outboards. Sold by Lithium Battery Supply.
If you run a modern outboard and a boat full of electronics, the Scorpion handles both jobs from one battery instead of a separate starting battery and house bank. It delivers 1300 cold cranking amps to start large 4-stroke and 2-stroke engines, and holds 120 amp-hours of deep-cycle capacity for graphs, sonar, live-imaging, pumps, and lights. Because it uses LiFePO₄ chemistry, it holds a flat voltage through most of its discharge, so electronics get steady power instead of the sag you see from lead-acid.
The battery management system is designed for the voltage spikes, cranking draw, and alternator output of modern outboards. The manufacturer states the Scorpion meets and exceeds Mercury Marine's current cranking specification and has been field-tested across Mercury, Yamaha, Suzuki, Evinrude, and MerCruiser platforms. If you want to shed weight while running heavy electronics, it is a strong single-battery solution.
If your engine is under factory warranty, confirm your specific engine model against your engine maker's current lithium-battery guidance before switching, since approval is engine-specific.
Will this battery work with my outboard?
The Scorpion is a dual-purpose cranking battery designed for modern high-output outboards. The manufacturer reports testing across Mercury Pro XS (4-stroke and 2-stroke), Yamaha SHO and 4-stroke, Yamaha HPDI, Mercury Verado 4-stroke, Suzuki 4-stroke, Evinrude 2-stroke, and MerCruiser 4-stroke engines. If your engine is under factory warranty, check your engine maker's current lithium guidance for your specific model first, since approval is engine-specific.
If the BMS shuts off, could it spike my alternator or electronics?
This is the most common concern with lithium cranking batteries, and it is a fair question. The risk people describe happens when a battery's BMS disconnects while the alternator is still charging. The Scorpion's BMS is built specifically for marine cranking and is designed to stay connected under the voltage spikes, cranking draw, and alternator output of modern outboards, supporting up to 200 A continuous. Many boaters run it as a straight replacement; on a critical single-battery setup, some add a lead-acid buffer or alternator protection for extra margin. If you are unsure about your specific charging system, contact us before installing.
Can one battery handle both cranking and my electronics?
Yes. That is what dual purpose means. The 1300 CCA covers engine starting, and the 120Ah of deep-cycle capacity powers graphs, sonar, live-imaging, pumps, and lights. Actual runtime depends on your total load as a rough guide, electronics pulling a combined 10 amps would run for roughly 10 hours before you need to recharge. LiFePO₄ also holds a flat voltage through most of its discharge, so electronics get steady power instead of the sag you see from lead-acid.
Do I need a special charger?
Use a lithium iron phosphate (LiFePO₄) charger or a charger with a lithium profile. A standard lead-acid or AGM charger may not reach the correct voltage or bring the battery out of BMS protection, and repeated improper charging can damage the pack. A lithium-compatible onboard or bench charger also keeps the battery maintained during storage.
Does it meet Mercury's lithium requirements?
The manufacturer states the Scorpion meets and exceeds Mercury Marine's current cranking specification. Mercury permits lithium iron phosphate cranking batteries only on an approved list of engine models, and only when the battery meets every point of their bulletin. Confirm your specific engine is on the current approved list with your dealer if warranty coverage is a factor for you.
Will using a lithium battery affect my engine warranty?
Engine makers handle this differently, and approval is tied to your exact engine model. When an approved lithium cranking battery is used on an approved engine, the engine maker generally states it will not void the engine warranty, but you should verify your model against the manufacturer's current guidance before relying on it. When in doubt, ask your dealer.
Can I charge it in cold weather?
This is not a self-heating model, so follow standard LiFePO₄ practice: do not charge it below freezing (32°F / 0°C), because charging a frozen cell can cause permanent damage. Discharging in the cold is generally fine within the battery's rated range. If you regularly fish or store in sub-freezing conditions, warm the battery before charging, or ask us about a heated battery option.
Will it fit my battery tray?
The Scorpion uses a standard Group 31 case measuring 13 × 6.8 × 8.8 in (330 × 173 × 225 mm), so it fits the same footprint as a typical Group 31 battery. Because tray sizes, terminal clearance, and hold-downs vary between boats, measure your compartment and confirm terminal orientation before ordering.
Can I wire two or more together?
You can wire units in parallel (positive to positive, negative to negative) to add amp-hour capacity. For 24V, 36V, or 48V series configurations, contact us first so we can confirm this model is suited to your setup.
How do I monitor the battery?
Bluetooth is built in. Download the MMLithium app for iOS or Android to read voltage, state of charge, and performance from your phone in real time.
How much lighter is it than lead-acid?
At 28 lb, it is roughly half the weight of a comparable Group 31 lead-acid battery, which removes a meaningful amount of weight from the back of the boat when you replace one or more batteries.
How should I store it in the off-season?
Lithium iron phosphate holds its charge well in storage, but any accessories left connected can slowly drain the battery over time. Keep it on a lithium-compatible maintenance charger, or charge it and then disconnect it during long storage, and store it out of sub-freezing conditions where possible.
What is the difference between this and the non-Bluetooth version?
This model (MML-13C120B) includes built-in Bluetooth so you can monitor voltage and state of charge in the MMLithium app. The non-Bluetooth version of the same battery has the same cranking and capacity ratings without the app monitoring feature.
What warranty does it come with?
The Scorpion is backed by Monster Marine Lithium's 15-year limited warranty. In years 0 to 5, a manufactured-defective battery is replaced or repaired at no cost to you with no charge-cycle limit; years 5 to 10 and 10 to 15 carry repair-based coverage with charge-cycle and cost provisions. Register your battery with the manufacturer within 60 days of purchase to activate full coverage. Contact us, Lithium Battery Supply, if you have any questions about coverage before you buy or Read Our Warranty Tab
