The MillerTech 12V 300Ah Sports Series (Heated) is a lithium iron phosphate (LiFePO4) deep-cycle marine battery built to run high-demand electronics and house loads through a full day on the water. With 300Ah of capacity and Bluetooth monitoring, it keeps fish finders, live sonar, livewell and bilge pumps, lights, radios, and other 12-volt gear powered without the mid-day drop-off common to lead-acid batteries.

Because LiFePO4 delivers close to its full rated capacity from charge to cutoff, one battery can cover a demanding electronics setup and still hold reserve power. It also runs 12-volt trolling motors, and it can be wired into 24V or 36V systems when you need higher voltage. Beyond the boat, it fits RV house power, solar energy storage, off-grid cabins, and backup power.

The built-in heater sets this model apart for cold-weather use. When temperatures reach freezing and a charger is connected, the heater warms the cells so the battery can charge safely in conditions that would normally prevent a standard lithium battery from charging. That makes it a practical choice for early-spring, late-fall, ice-season, and cold-climate boaters and off-grid users.

It is built with a high-output BMS, pure brass terminals, dual stainless steel breathable vents, a sealed marine-grade case, and an integrated carry handle, and it is backed by a 10-year no-questions-asked warranty.

Features & Benefits

• 300Ah / 3,840Wh capacity: a large energy reserve that runs electronics, accessories, and 12-volt loads through long days, so you spend less time watching the charge level.
  
  
• Built-in self-heating: the internal heater engages in freezing conditions using power from your connected charger, letting the battery charge safely in cold weather when a standard lithium battery cannot.
  
  
• Low-temperature charging protection: the BMS guards the cells against cold-charge damage, protecting long-term battery health.
  
  
• Bluetooth monitoring: the MillerTech App shows real-time state of charge, voltage, and current draw, giving you an accurate picture of remaining power on the water.
  
  
• High-output BMS with 150A continuous rating: steady output under heavy load, with protection against overcharge, over-discharge, short circuit, and over-temperature.
  
  
• LiFePO4 deep-cycle chemistry: provides close to full usable capacity and a long service life, unlike lead-acid batteries that should only be discharged about halfway.
  
  
• Lightweight for its capacity: at 62.3 lbs it replaces a much heavier bank of lead-acid batteries of similar usable capacity.
  
  
• Marine-grade construction: sealed case, pure brass terminals for strong conductivity, dual stainless steel vents to reduce condensation, and an integrated carry handle for easier installation.
  
  
• 10-year no-questions-asked warranty: long-term coverage from the manufacturer, including shipping for repair or replacement during the warranty period.

Applications & Compatibility

Recommended applications

• Marine electronics and house power (fish finders, GPS, live and forward-facing sonar, VHF radios, stereo systems)
• Marine accessories (livewell and aerator pumps, bilge pumps, deck and cabin lighting)
• 12-volt trolling motors on a single battery, or 24V/36V systems when wired in series
• RV and camper house power
• Solar energy storage and off-grid systems
• Backup and emergency power

Suitable for

• Bass boats, center consoles, bay boats, and pontoons (electronics and house power)
• Jon boats and aluminum boats running 12-volt trolling motors
• RVs, campers, and vans
• Off-grid cabins and solar setups
• Backup power systems

Series and parallel compatibility

• Wire in parallel to keep 12-volt output and add capacity for longer runtime.
• Wire in series with up to four batteries for 24V, 36V, or 48V systems; capacity stays the same as a single battery. MillerTech recommends parallel wiring for longer battery life where possible, and offers dedicated 24V, 36V, and 48V batteries for higher-voltage needs.

Fitment

• Group 50 case measuring 13.5 in x 9.6 in x 10.5 in. It will not fit a standard Group 24, 27, or 31 tray. A battery tray sized for the 12V 300Ah footprint is available separately.

Specifications

FAQ