Spend the day fishing, not worrying about your battery. The MillerTech 12V 190Ah Dual Purpose lets one battery do two jobs: fire up your outboard the moment you turn the key, then run every screen and pump on your boat from first light to the last cast.

That means starting a big motor, verified by MillerTech for Mercury 4-stroke outboards up to 250hp, and still having the reserve to keep multiple graphs, forward-facing sonar, livewells, and aerators running all day. Anglers regularly fish a full 8-hour tournament with everything on and come back with charge to spare. No mid-day power anxiety, no cutting the trip short, no dead battery at the ramp.

It also cleans up your rig. Instead of a heavy starting battery plus a separate deep-cycle bank, you run one Group 31 battery that weighs about 42 lbs, far less than the lead-acid setup it replaces, so your boat sits lighter and gets on plane easier. Built-in Bluetooth shows exactly how much power you have left right on your phone, so there is never a guess.

And it is a buy-once decision. With a long rated cycle life and a 10-year warranty behind it, this battery is built to outlast several sets of lead-acid. If you want one dependable battery to both start your motor and power your electronics, on a bass boat, an offshore or center console rig, or as house power in an RV, this is built for exactly that.

Features & Benefits

• 1500 Cold Cranking Amps (CCA): Provides the burst of current needed to start large outboards. Verified by MillerTech for Mercury 4-stroke motors up to 250hp, so you get reliable starts.
  
  
• 190Ah Reserve Capacity: Supplies steady power to graphs, forward-facing sonar, livewell pumps, and 12V electronics, letting you run your setup through a full day on the water.
  
  
• Dual Purpose Design: Combines cranking and deep-cycle capability in one battery, which can reduce the number of batteries and total weight in your boat.
  
  
• LiFePO4 Prismatic Cells: Deliver a flat voltage curve, keeping electronics running consistently as the battery discharges rather than fading like lead-acid.
  
  
• Long Cycle Life: Rated for up to about 8000 cycles at shallow depth of discharge and around 2000 cycles at full depth of discharge, measured to 80% remaining capacity, which supports years of regular use.
  
  
• Smart Battery Management System (BMS): Protects against over-charge, over-discharge, over-current, and unsafe high and low temperatures, and passively balances the cells at the top of each charge to help extend battery life.
  
  
• Low-Temperature Charging Protection: Prevents charging in freezing conditions to protect the cells, useful for cold-weather and early-season use.
  
  
• Bluetooth Monitoring: Connects to the MillerTech app to show state of charge, voltage, real-time current, temperature, and cycle count, and can monitor multiple MillerTech batteries at once.
• 98% Efficiency: Makes nearly all stored energy usable, supporting longer run times and faster charging.
  
  
• Sealed, Water-Resistant Case: Built with a thick rubber gasket and a stainless steel breather vent to help guard against moisture and condensation. Keep it out of direct rain, spray, and standing water.
  
  
• Recloseable Heavy-Duty Case: Allows access for service years down the line, with molded strap grooves to keep hold-downs seated securely.
  
  
• Heavy-Duty M8 Terminals: Reduce heat build-up when the application is drawing maximum power. Torque to 10 ft-lbs with a torque wrench for a secure connection.
  
  
• UL 1973 Certified: Independently tested to ANSI/CAN/UL 1973:2022 Ed.3, a safety standard that evaluates the full battery system, not just the cells.
  
  
• BCI Group 31 Footprint, 42 lbs: Fits standard Group 31 trays and is lighter than a comparable lead-acid battery.
  
  
• 10-Year Warranty: Backed by MillerTech, with no warranty registration required.

Compatibility & Applications

This battery is a dual purpose starting and deep-cycle battery for marine and RV use. Use the guidance below to confirm it fits your setup.

Recommended Applications

• Bass and multi-species boats using one battery for starting and electronics
• Offshore and center console boats
• RV 12V house and deep-cycle power

Suitable For

• Starting outboard motors, verified for Mercury 4-stroke up to 250hp
• Running fish finders, forward-facing sonar, multiple graphs, livewell and aerator pumps, stereo, and other 12V electronics
• Providing house and deep-cycle power in RVs

Series and Parallel

The battery can be connected in series or parallel. Up to 4 batteries can be wired in series to build a 24V, 36V, or 48V system, or up to 4 in parallel for more capacity. Match battery voltages before connecting and use appropriate fuses or breakers. In a series bank, charge with a multi-bank charger, or fully charge each battery individually about every 10 cycles to keep the pack balanced.

Compatibility Notes

• Use a LiFePO4-compatible charger. A standard lead-acid charger may not fully charge a lithium battery because it stops at a lower voltage.
• Do not charge with an unregulated alternator or a non-lithium charger.
• Fits standard BCI Group 31 battery trays at 13” x 6.75” x 9”.
• For outboard brands other than Mercury, confirm your motor’s charging system is regulated and rated for lithium batteries before installing. Some manufacturers advise checking the regulated charging output voltage first.

Charging & Compatible Chargers

Charging is simple with the right charger. Use a lithium (LiFePO4) charger with a 14.2–14.6V charging profile. A standard lead-acid charger may stop at a lower voltage and only partially charge the battery, and in some cases can trip the BMS. If your charger is labeled for lead-acid only, or has a desulfation or repair mode, use a LiFePO4 charger instead.

First charge

The battery ships partially charged due to shipping regulations. Charge it fully before installing it in your application.

Charge rate and time

MillerTech lists a recommended charge current of about 50A and a maximum charge current of 150A for this battery, so every MillerTech charger falls comfortably within a safe, cell-friendly range. Approximate charge time from a low battery to full:

• 10A charger (1210C): about 19 hours
• 20A charger (1220C or 1220M on-board): about 9 to 10 hours
• 15A per bank (multi-bank chargers): about 13 hours per battery

These are full-charge estimates from a low battery. In normal use you rarely start from empty, so real recharge times are shorter. You can watch charge progress live in the MillerTech app.

Settings for programmable chargers

• Bulk and absorption voltage: 14.2 to 14.6V, held about 15 to 20 minutes per battery
• Float: not required; 13.5 to 13.8V may be used when connected to shore power
• Equalization: turn off, or set below 14.6V and 0 hours
• Temperature compensation: turn off or set to 0, since it can trigger the BMS protection

Charging on the water

As a dual purpose cranking battery, it is designed to be maintained by your outboard’s regulated charging system while you run, the same way a starting battery is. After a heavy day running electronics, top it off with a LiFePO4 shore charger. To charge while operating a 12V plus 24V or 12V plus 36V system, MillerTech’s On The Run Dark Speed chargers are built for that.

Cold weather

Do not charge below freezing. The battery’s low-temperature charging protection prevents this automatically. Its charge temperature range is 25°F to 131°F; allow the battery to warm above 32°F before charging.

Compatible MillerTech chargers

MillerTech confirms the following chargers are compatible with the 12V 190Ah Dual Purpose (12190-DP):

The MillerTech 12V 5A charger (125C) is not recommended for this battery. It is intended for smaller batteries and would charge a 190Ah battery very slowly. Any quality LiFePO4 charger with a 14.2 to 14.6V profile will also work.

Specifications

FAQs