The Monster Marine Lithium "Beast 2.0" is a 12V 170Ah dual-purpose lithium (LiFePO4) cranking battery that starts your outboard and runs a full day of electronics from a single Group 31 case. It replaces a traditional 12V AGM or lead-acid starting battery, cuts weight out of the back of the boat, and holds steady voltage from the first cast to the last.
With 1500 cold cranking amps for strong starts and 170 amp-hours of usable energy, the Beast 2.0 is built for anglers running heavy electronics packages multiple graphs, forward-facing sonar, 360 imaging, livewells, pumps, shallow-water anchors, and lights, without the voltage drop that lead-acid batteries suffer as the day goes on. It is well suited to bass boats, bay boats, center consoles, and tournament rigs where a standard starting battery struggles to keep up with the engine and a growing electronics load at the same time. Built-in Bluetooth lets you check state of charge and battery health on your phone through the MMLithium app.
The simple benefit: instead of choosing between a strong cranking battery and a large house battery for electronics, the Beast 2.0 is designed to handle both jobs from one high-capacity lithium battery starting the engine and running your electronics all day.
Monster Marine Lithium is an angler-founded company that builds LiFePO4 batteries for tournament and everyday fishing use, and its batteries are run in competition by MLF Bass Pro Tour pro Zack Birge. The Beast 2.0 is the redesigned version of their original Beast cranking battery, using Grade A LiFePO4 cells and an updated battery management system.
Features and Benefits
One battery for starting and electronics
The Beast 2.0 delivers the high burst of current needed to start large outboards, plus 170Ah of deep-cycle capacity and up to 200A continuous discharge for your electronics. In many rigs that lets one battery do the work of a separate starting battery and house battery.
No voltage sag under load
Unlike lead-acid and AGM batteries, which lose voltage as they drain, LiFePO4 holds a stable voltage through most of its charge. That helps keep power steady to your graphs, sonar, and pumps deeper into the day, rather than tapering off the way lead-acid does as it runs down.
Serious weight savings
At 39 lbs, the Beast 2.0 weighs roughly half of a comparable Group 31 AGM battery. Taking that weight out of the stern can help with hole shot and handling, and makes the battery much easier to lift in and out.
Bluetooth monitoring
The built-in Bluetooth module connects to the free MMLithium app so you can see voltage, state of charge, and battery health in real time from your phone, no separate gauge to wire in.
Advanced BMS protection
An internal battery management system protects the cells against overcharge, over-discharge, over-current, high temperature, and short circuits, and balances the cells for consistent performance and long life.
Group 31 drop-in fitment
The Beast 2.0 is built in a standard Group 31 case (13 × 6.8 × 8.66 in) and drops into a standard Group 31 tray. Combination top-post and M8 bolt terminals make it easy to connect factory cables or ring terminals.
Long service life
Rated for 4000+ charge cycles, LiFePO4 chemistry lasts far longer than lead-acid, which typically delivers a few hundred cycles before capacity fades.
Compatibility and Fitment
Engine compatibility
Monster Marine Lithium states the Beast 2.0 has been tested for over a year on a wide range of outboards, including Mercury Pro XS 4-stroke and 2-stroke, Mercury Verado 4-stroke, MerCruiser 4-stroke, Yamaha 4-stroke and SHO 4-stroke (older and newer), Yamaha HPDI, Suzuki 4-stroke, and Evinrude 2-stroke. MML also states the Beast 2.0 is built to meet and exceed Mercury Marine's latest lithium cranking specification bulletin.
One point worth being clear on: testing by the battery maker is not the same as formal approval by your engine manufacturer.
It does not guarantee your engine's warranty will cover a related repair, and it does not confirm fitment for every horsepower and model year.
Because engine manufacturers set their own battery policies, always confirm your specific engine's requirements before switching to a lithium cranking battery.
Mercury Marine publishes a list of approved engines and minimum specifications for lithium starting batteries in its service bulletin; check that your engine is on that list.
Mercury's specification calls for a LiFePO4 cranking battery with at least 800 cranking amps, a maximum charge voltage of 14.8V, and an IP67 ingress rating. The Beast 2.0's 1500 CCA and 14.6V charge point fall within those cranking and charge-voltage limits.
Yamaha's published position is that it does not endorse lithium starting batteries for its outboards, and using one may affect engine warranty coverage on related components.
If your engine is under warranty, verify your engine maker's current guidance before installing any lithium cranking battery.
Electronics it can run
With 170Ah of capacity and up to 200A of continuous discharge, the Beast 2.0 is sized for boats running large electronics packages multiple graphs, forward-facing sonar such as LiveScope, Mega 360 imaging, shallow-water anchors, livewell and bilge pumps, and lighting, while still handling engine starting.
Approximate runtime
These figures are rough estimates of how long a full 170Ah battery will run at a steady current draw. Real fishing loads vary as pumps, sonar, and displays cycle on and off, so treat these as a guide rather than a guarantee. On a dual-purpose battery, leave enough reserve to start the engine at the end of the day.
| Steady load |
Approximate runtime |
| 10 A |
Around 17 hours |
| 20 A |
Around 8.5 hours |
| 30 A |
Around 5.5 hours |
Fitment
The Beast 2.0 fits a standard Group 31 battery tray. Dimensions are 13 in long × 6.8 in wide × 8.66 in tall (330 × 173 × 220 mm). Terminals are a combination top-post and M8 bolt design.
Charging
Charger requirements
The Beast 2.0 charges to 14.6V. A LiFePO4-capable charger is the best choice. Monster Marine Lithium also states that its 12V batteries can be charged with a standard onboard AGM charger, provided the profile stays within the battery's 14.6V charge range and does not run an equalization or desulfation stage. Do not use a charger that exceeds this voltage.
Charging from your engine
If you plan to charge from your outboard's alternator while running, confirm your engine's regulated charging output falls within the battery's charge range and follow your engine manufacturer's guidance on charging lithium batteries. Mercury's lithium specification sets a maximum charge voltage of 14.8V and alternator limits for approved engines; staying within those limits protects both the battery and the charging system.
Fast recharge
LiFePO4 batteries accept a charge faster than lead-acid, so recovery time between trips is shorter. A higher-amperage lithium-capable charger will refill the battery more quickly; match charger amperage to how fast you need to turn the boat around.
Specifications
| Model |
MML-15170JB |
| Battery chemistry |
Lithium Iron Phosphate (LiFePO4), Grade A cells |
| Nominal voltage |
12.8V |
| Nominal capacity |
170Ah |
| Energy |
2176 Wh |
| Cold cranking amps (CCA) |
1500 |
| Continuous discharge current |
200A max |
| Charge voltage |
14.6V |
| Cycle life |
4000+ cycles |
| Weight |
39 lbs |
| Dimensions (L × W × H) |
13 × 6.8 × 8.66 in (330 × 173 × 220 mm) |
| Case size |
Group 31 |
| Terminal type |
Top post & M8 bolt combo |
| Monitoring |
Built-in Bluetooth via MMLithium app |
| Primary use |
Dual-purpose starting and deep-cycle, 12V marine |
| Certifications |
UN/DOT 38.3; UL listed cells; IEC 62133-2017; CE |
| Warranty |
5-year free replacement (tiered coverage through 15 years) |
Safety and Certifications
Lithium Iron Phosphate (LiFePO4) is one of the most thermally stable lithium chemistries, which is why it is the standard choice for marine cranking and deep-cycle use. The Beast 2.0 uses Grade A LiFePO4 cells and an internal battery management system.
Battery management system (BMS)
The internal BMS protects the cells against overcharge, over-discharge, over-current, high temperature, and short circuits, and shuts the battery off to protect the cells if it detects unsafe operating conditions. It also balances the cells for consistent performance across the battery's life.
Certifications
Monster Marine Lithium states its batteries carry the following certifications and conform to the following safety and transport standards:
- UN/DOT 38.3 transport safety testing, including 49 CFR 172.704(a) & (3), IATA DGR 1.5.2 & 1.5.2.2(c), IMDG Code 1.3.1.2 & 1.3.1.4, and 29 CFR 1910.1200(h)(3)(i)-(iii)
- UL listed cells
- IEC 62133-2017 cell safety
- ISO 9001:2008 quality management
- ISO 14001:2004 environmental management
- CE
Frequently Asked Questions
Will the Beast 2.0 work with my outboard engine?
Monster Marine Lithium states the Beast 2.0 has been tested for over a year on a wide range of outboards, including Mercury Pro XS (4-stroke and 2-stroke), Mercury Verado, MerCruiser, Yamaha 4-stroke and SHO, Yamaha HPDI, Suzuki 4-stroke, and Evinrude 2-stroke. Engine manufacturers set their own battery policies, so confirm your specific engine's requirements before switching to a lithium cranking battery.
Can I use it on a Yamaha outboard?
Monster Marine Lithium lists Yamaha 4-stroke, SHO, and HPDI among the engines it has tested the Beast 2.0 on. However, Yamaha's published position is that it does not endorse lithium starting batteries for its outboards, and using one may affect warranty coverage on related components. If your Yamaha is under warranty, contact Yamaha or your dealer for their current guidance before installing any lithium cranking battery.
Does it meet Mercury Marine's lithium specification?
Monster Marine Lithium states the Beast 2.0 meets and exceeds Mercury Marine's latest lithium cranking specification bulletin. The battery's 1500 CCA and 14.6V charge point fall within Mercury's published minimum cranking and maximum charge-voltage requirements. Mercury approves lithium cranking batteries only for specific engines listed in its service bulletin, so confirm your engine is on that list before installing.
What does 1500 CCA mean on a lithium battery?
Cold cranking amps (CCA) is a rating that originated with lead-acid batteries, and it is provided here as a familiar cross-reference to the starting power you are used to. What matters in practice is that the Beast 2.0 delivers a strong burst to crank large outboards and sustains up to 200A of continuous discharge to run electronics while holding steady voltage instead of sagging the way lead-acid does as it drains.
Can one battery both start my engine and run my electronics?
Yes. The Beast 2.0 is a dual-purpose battery designed to crank the engine and provide 170Ah of deep-cycle capacity for electronics. In many rigs it can replace both a separate starting battery and a 12V house battery. If you run an unusually large electronics load, you can add capacity by connecting a second battery in parallel.
How many graphs and electronics can it run?
With 170Ah of capacity and up to 200A of continuous discharge, the Beast 2.0 is sized for large electronics packages, including multiple graphs, forward-facing sonar such as LiveScope, Mega 360 imaging, shallow-water anchors, livewell and bilge pumps, and lighting, while still starting the engine. Actual runtime depends on how many devices you run and how hard you run them.
Will the BMS shut off and stop my motor while I'm running?
The Beast 2.0 uses an updated battery management system tuned for modern 4-stroke charging. The scenario anglers worry about is charging a lithium battery to 100 percent, then making a long run so the charging system keeps pushing voltage into a full battery. To avoid this, confirm your engine's regulated charging output stays within the battery's charge range, and follow your engine manufacturer's guidance for charging lithium batteries. If your engine is not approved for lithium cranking batteries, keep a lead-acid or AGM starting battery.
Can I charge it from my outboard's alternator?
Many anglers charge lithium cranking batteries from the engine while running, but this depends on your engine. Confirm your alternator's regulated output voltage falls within the battery's 14.6V charge range and follow your engine manufacturer's guidance. Mercury's lithium specification sets a maximum charge voltage of 14.8V and alternator limits for its approved engines.
Can I charge it in cold weather?
Like standard LiFePO4 batteries, the Beast 2.0 should not be charged below freezing, because charging cold cells can cause permanent damage. Discharging in the cold is not the concern charging is. Monster Marine Lithium's guidance for cold climates is to fully charge the battery before winter, remove it from the boat, and store it in a temperature-controlled space such as a house or garage, avoiding freezing temperatures. In areas that stay above freezing, you can leave it in place charged to 100 percent with the wiring disconnected. If you regularly need to charge in freezing conditions, warm the battery in a protected location first.
What charger do I need?
A LiFePO4-capable charger is the best choice. Monster Marine Lithium also states that its 12V batteries can be charged with a standard onboard AGM charger, as long as the profile stays within the battery's 14.6V charge range and does not run an equalization or desulfation stage. Do not use a charger that exceeds this voltage. A higher-amperage lithium-capable charger will recharge the battery faster between trips.
Does it fit a standard Group 31 tray?
Yes. The Beast 2.0 is built in a Group 31 case measuring 13 × 6.8 × 8.66 in (330 × 173 × 220 mm) and drops into a standard Group 31 tray. It uses combination top-post and M8 bolt terminals.
Can I connect two in parallel?
Yes. Monster Marine Lithium states additional batteries can be added in parallel to increase capacity for higher electrical demand. Parallel wiring keeps the system at 12V while adding amp-hours.
How much lighter is it than my current battery?
The Beast 2.0 weighs 39 lbs, roughly half the weight of a comparable Group 31 AGM battery. Taking that weight out of the stern can help with hole shot and handling, and makes the battery much easier to lift.
How do I monitor the battery?
The Beast 2.0 has a built-in Bluetooth module that connects to the free MMLithium app, available for Apple and Android devices. The app shows voltage, state of charge, and battery health in real time, so you do not need a separate gauge.
Is it waterproof, and what certifications does it carry?
The Beast 2.0 is built for the marine environment and uses an internal BMS for protection. Monster Marine Lithium states its batteries conform to UN/DOT 38.3 transport safety testing and carry UL listed cells, IEC 62133-2017 cell safety, ISO 9001:2008, ISO 14001:2004, and CE. Mount the battery securely and keep terminal connections tight, as loose terminals can cause heat buildup.
What is the warranty?
The strongest part of the coverage is the first 5 years: a defective battery is replaced with a new one at no cost, with no charge-cycle limit (you cover return shipping). This is not a full 15-year replacement warranty. After year 5, coverage is reduced years 5 to 10 are a repair tier with a 2,000-cycle limit and you pay shipping, and years 10 to 15 are prorated. Register the battery with Monster Marine Lithium after purchase to activate coverage. See our warranty page for full terms.
