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Group 31 Dual Purpose Lithium Battery: 12V 180Ah Starts and Runs
Short answer: A Group 31 dual purpose lithium battery like the Pro-Guide 31M180-DP is a 12.8V, 180Ah LiFePO4 battery that cranks your engine at 1,000 CCA (lead-acid equivalent) and stores 2,304 watt-hours for your fish finders, livewell and accessories, all from a standard-height Group 31 case (13.07 x 6.93 x 8.9 in) that weighs 41.89 lb. One battery replaces the separate starting and house batteries many boats carry, and it adds Bluetooth monitoring, a built-in heater and NMEA 2000 compatibility.
Most boats are wired with a cranking battery for the outboard and, if the owner is lucky, a second battery for electronics. A dual purpose lithium battery changes that math. Below we explain what a Group 31 dual purpose lithium battery is, how much cranking and runtime the 31M180-DP really gives you, how it compares with a Group 31 AGM, how to charge it from shore power and your alternator, and how to decide between it and its taller sibling, the 31M235-DP.
Key Takeaways
- Starts and runs: 1,000 CCA lead-acid equivalent (800A for 8 seconds, 1,000A for 5 seconds) plus 180Ah and 2,304Wh of deep cycle capacity.
- Fits a standard Group 31 space: 13.07 x 6.93 x 8.9 in, so it drops into Group 31 trays and boxes without the extra height of a "tall" case.
- Light for its capacity: 41.89 lb (19 kg).
- Smart features: Bluetooth monitoring, built-in heater, NMEA 2000 compatible, state of charge gauge and BMS reset.
- Long life: more than 3,000 cycles at 100% depth of discharge, more than 6,000 at 80%, IP67 rated.
- Warranty: 3-year free replacement and 10-year pro-rata coverage.
What Is a Dual Purpose Lithium Battery?
Marine batteries usually fall into three jobs. A starting (cranking) battery delivers a big burst of current for a few seconds to turn over an engine, then gets recharged by the alternator. A deep cycle battery delivers a steady, smaller current for hours to run trolling motors, electronics and pumps. A dual purpose battery is built to do both.
With lead-acid and AGM, "dual purpose" has always been a compromise: thick plates crank well but don't like deep discharges, and thin plates cycle well but can't deliver the same burst. Lithium iron phosphate (LiFePO4) chemistry narrows that trade-off. A LiFePO4 battery holds its voltage under load, can use nearly all of its rated capacity, and lasts thousands of cycles, which lets one battery handle both the cranking load and the house load.
"Group 31" is the Battery Council International (BCI) case size. It describes the outside dimensions, not what's inside, which is why a Group 31 dual purpose lithium battery can slide into the same tray that held your old Group 31 AGM. The Pro-Guide 31M180-DP is our 180Ah dual purpose model in a standard-height Group 31 case.
Pro-Guide 31M180-DP Specifications
| Model / SKU | Pro-Guide 31M180-DP (PGL31M180-DP) |
| Battery type | Dual purpose (starting + deep cycle), LiFePO4 |
| Nominal voltage | 12.8V |
| Capacity / energy | 180Ah / 2,304Wh |
| Cranking | 1,000 CCA lead-acid equivalent (PbEq); 800A for 8 s, 1,000A for 5 s |
| Reserve capacity | 309 min at 25A to the Pro-Boost safety cut-off; 344 min to the low-voltage cut-off |
| Cycle life | 3,000+ cycles at 100% DoD, 6,000+ at 80% DoD |
| Discharge current | 36A standard, 180A continuous, 10V cut-off |
| Charge current | 10A to 36A standard, 90A maximum continuous, 14.4V charge cut-off |
| Alternator charging | 200A charge acceptance, 14.8V maximum, peak 1.65C for 1 minute |
| Charging temperature | -4°F to 131°F (-20°C to 55°C), built-in heater |
| Discharge temperature | -4°F to 140°F (-20°C to 60°C) |
| Features | Bluetooth, NMEA 2000 compatible, state of charge gauge, BMS reset, removable handle |
| Protection | IP67 |
| Terminals | 3 x M8 internal thread |
| Dimensions | 13.07 x 6.93 x 8.9 in (332 x 176 x 226 mm) |
| Weight | 41.89 lb (19 kg) |
| Warranty | 3-year free replacement, 10-year pro-rata |
Want every number? Download the 31M180-DP data sheet (PDF).
The 31M180-DP in its standard-height Group 31 case. The front label lists 12.8V, 1,000 CCA (PbEq), 180Ah and 2,304Wh.
Can One Battery Start Your Engine and Run Your Electronics?
Yes, and the numbers show why. Start with cranking. The 31M180-DP is rated at 1,000 CCA lead-acid equivalent, and its data sheet lists 800 amps for 8 seconds and 1,000 amps for 5 seconds. A normal outboard start lasts a second or two, so a start uses a tiny slice of a 180Ah battery. Because LiFePO4 holds its voltage, the battery is also far less likely to sag after a long day of running electronics, which is exactly when a tired lead-acid starting battery lets you down at the ramp.
Now the house side. For a rough runtime estimate, divide 180Ah by your load in amps:
| Load | Typical draw | Estimated runtime on the 31M180-DP |
| Single fish finder / chartplotter | About 2A | About 90 hours |
| Multiple graphs plus live sonar | About 10A | About 18 hours |
| Heavier accessory load (pumps, lights, graphs) | About 30A | About 6 hours |
| Steady 25A (reserve capacity test) | 25A | 309 minutes to the Pro-Boost safety cut-off |
Real runtime depends on the load, temperature and how deep you discharge. One customer reported running two graphs and a livewell continuously for eight hours on the first trip and still had 79% charge left. That kind of margin is why many anglers stop carrying a separate electronics battery once they switch to a dual purpose lithium.
The one rule of thumb: keep enough charge to start the engine. The data sheet lists two cut-offs at a steady 25A: the Pro-Boost safety cut-off at 309 minutes, then the low-voltage cut-off at 344 minutes. If the battery does shut off on low charge, the label's "Restart on Low SOC" step (hold TEST for 3 seconds) temporarily wakes it for 2 minutes. If the battery has a fault, it shuts off again immediately.
Group 31 Dual Purpose Lithium vs. AGM
If you are pricing a new Group 31 AGM, here is how it compares with the 31M180-DP in the same case size.
| Factor | Pro-Guide 31M180-DP (LiFePO4) | Typical Group 31 dual purpose AGM |
| Usable capacity | Nearly all of 180Ah | About 50% of rated capacity to protect battery life |
| Weight | 41.89 lb | Usually heavier for less usable capacity |
| Cycle life | 3,000+ at 100% DoD | Typically a few hundred cycles |
| Voltage while cranking after a long day | Stays flat until nearly empty | Sags as the battery drains |
| Monitoring | Bluetooth, NMEA 2000 compatible, onboard gauge | Usually a separate voltmeter |
| Cold-weather charging | Built-in heater, -4°F to 131°F charging range | No heater; cold reduces available capacity |
| Warranty | 3-year free replacement, 10-year pro-rata | Usually 1 to 3 years |
The deciding factor for most boaters is usable capacity. A Group 31 AGM is normally discharged only about halfway to protect its life, and its voltage falls as it drains, so the same battery that ran your graphs all day may crank slowly at the end of it. The 31M180-DP gives you nearly its full 180Ah, holds its voltage, and lasts thousands of cycles, so it usually costs less per cycle over its life even though it costs more up front.
What Is the 31M180-DP Best For?
The 31M180-DP is built for boats that need one battery to start the engine and power electronics, in a standard-height Group 31 space. Good fits include:
- Bass boats and fishing boats with an outboard: crank the motor and run graphs, live sonar, livewells and pumps from one battery. If you'd still rather isolate your electronics, read Should You Run a Separate Battery for Your Boat Electronics?
- Replacing an old Group 31 starting or house battery: same footprint, no rebuilding your compartment. The NOCO Group 31 Battery Tray and the Group 24-31 Plastic Battery Box are matched add-ons.
- Networked electronics: it is NMEA 2000 compatible, so it can share battery data on a marine electronics network. Learn more in What Is NMEA and Why Does It Matter for Your Battery Setup?
- Complete boat systems: pair it with a lithium trolling motor pack and an onboard charger in one order: the 12V 180Ah & 24V 90Ah Bundle (with a PGC-1224 2-bank charger) or the 12V 180Ah & 36V 60Ah Bundle (with a PGC-1236X 2-bank charger). See One Pack or Three? for choosing the trolling motor side.
- RV and outdoor systems: 2,304Wh of deep cycle capacity for lights, fans, pumps and devices.
For clean electronics wiring, the Bass Tank Power Harness is a popular add-on.
The top label of the 31M180-DP shows its three M8 terminals, the TEST button with state of charge and Bluetooth status lights, and the sleep and wake-up instructions.
How to Charge the 31M180-DP
As a dual purpose battery, the 31M180-DP charges two ways: from a shore-power charger at the dock or in the garage, and from your engine's alternator while you run.
Shore charging. Charge time is roughly the capacity divided by the charger's output:
- 10A charger bank: about 18 hours from empty, for example with the 12/16V 10A 1-Bank Battery Charger, which has a 12V lithium profile.
- 20A charger bank: about 9 hours from empty.
- 30A charger: about 6 hours from empty with the Pro-Guide 12V 30A Lithium Battery Charger.
- 36A, the top of the standard range: about 5 hours. 90A maximum continuous: about 2 hours.
Alternator charging. The data sheet lists 200A charge acceptance from an engine alternator at up to 14.8V, with a peak acceptance of 1.65C for 1 minute. That is what keeps the battery topped up between starts on a running day.
Charging rules from the battery label:
- Keep charging voltage between 14.0V and 15.0V, for both the vehicle and the battery charger. Never exceed 15.0V.
- Don't use a charger with an automatic "desulfation" function. That mode is for lead-acid batteries.
- Stop if it gets hot. If the battery becomes hot to the touch, stop charging and let it cool before resuming.
- Know your voltages. The label lists 13.8V as 100% charged and 13.1V as 20% charged.
Cold weather is less of a worry than with most lithium batteries: the built-in heater gives the 31M180-DP a charging range of -4°F to 131°F (-20°C to 55°C). For storage, keep it between 23°F and 113°F (-5°C to 45°C).
Setup Tips Before Your First Trip
Wake it up
The 31M180-DP ships in sleep mode to save power. Hold the TEST button for 3 seconds: the green lights (75%-100%) flash three times, then the battery turns on. To put it back to sleep for storage, hold TEST for 3 seconds until the red light flashes three times and the battery shuts off.
Check state of charge
Quickly press TEST to see the state of charge lights, or check the battery over Bluetooth with the Pro-Guide Power app (iOS).
Plan for the off-season
The label recommends disconnecting the battery cables when the boat sits unused and putting the battery into sleep mode with the TEST button.
Mount it securely and keep terminals tight
IP67 means dust-tight and protected against temporary immersion, but it still belongs in a tray or box with a hold-down. Keep the three M8 terminals clean and securely fastened; battery corrosion preventative spray helps on the water.
31M180-DP vs. 31M235-DP: Which Should You Choose?
Both are Pro-Guide 12.8V dual purpose LiFePO4 batteries rated at 1,000 CCA lead-acid equivalent, with the same 13.07 x 6.93 in footprint, Bluetooth, heater and NMEA 2000 compatibility. The difference is height and capacity.
| Spec | 31M180-DP | 31M235-DP |
| Capacity / energy | 180Ah / 2,304Wh | 235Ah / 3,008Wh |
| Continuous discharge | 180A | 200A |
| Case / height | Group 31, 8.9 in | Group 31 Tall, 10.83 in |
| Weight | 41.89 lb | 52.91 lb |
Choose the 31M180-DP if your compartment or lid only clears a standard Group 31, or if you want to save about 11 lb. Choose the 31M235-DP if you have about 1.9 in of extra height and run a big electronics package that benefits from the extra 55Ah.
Frequently Asked Questions
What is a Group 31 dual purpose lithium battery?
It is a lithium battery in the BCI Group 31 case size that can both start an engine and power deep cycle loads. The Pro-Guide 31M180-DP is a 12.8V, 180Ah LiFePO4 example rated at 1,000 CCA lead-acid equivalent.
How many cranking amps does the 31M180-DP have?
It is rated at 1,000 CCA lead-acid equivalent (PbEq). The data sheet lists 800 amps for 8 seconds and 1,000 amps for 5 seconds.
How long will the 31M180-DP run my electronics?
Divide 180Ah by your load: about 90 hours at 2A, about 18 hours at 10A and about 6 hours at 30A. Reserve capacity is 309 minutes at 25A before the Pro-Boost safety cut-off.
Will the 31M180-DP fit in a Group 31 battery box?
Yes. It uses a standard Group 31 case, 13.07 x 6.93 x 8.9 in, so it fits Group 31 boxes and trays. Check length and terminal clearance in your compartment before installing.
Can my alternator charge a lithium dual purpose battery?
Yes. The 31M180-DP data sheet lists 200A alternator charge acceptance at up to 14.8V. The label says both vehicle and charger should limit voltage to 14.0V to 15.0V.
Can I charge the 31M180-DP in cold weather?
Yes, within limits. It has a built-in heater and a charging range of -4°F to 131°F (-20°C to 55°C).
Is the 31M180-DP NMEA 2000 compatible?
Yes. It is NMEA 2000 compatible and also has Bluetooth monitoring and an onboard state of charge gauge.
What warranty comes with the 31M180-DP?
A 36-month (3-year) free replacement warranty and 120 months (10 years) of total pro-rata coverage.
Upgrade to Group 31 Dual Purpose Lithium
If your boat has a standard Group 31 slot and you're tired of juggling a starting battery and a house battery, the Pro-Guide 31M180-DP gives you 1,000 CCA of cranking and 180Ah of all-day power in one case. It is built for anglers who want to stop worrying about whether the motor will start after a long day of graphs and live sonar, and it is backed by a 10-year warranty and a team that will help you plan the whole system.
Not sure which battery or charger fits your boat? Call our team at 1-800-827-3232 or browse all dual purpose lithium batteries and battery chargers.
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