36V 50AH Sport Series Lithium Battery w/ Bluetooth (3650-BT)

From an engineers point of view, using a 36V battery vs 3x 12V batteries is absolutely a no brainer. 36V batteries have electronics built in specifically designed for 36V applications, creating a true, no drama set up that will power your adventures for many years. 3x 12V can become misbalanced causing them to not work together in sync, causing you headaches that you shouldn’t have to deal with. Lithium batteries should simplify and eliminate battery stress, not cause you more! We take that assignment personally and are determined to make it a reality.

THE MILLERTECH® SPORT SERIES LITHIUM BATTERY
10 YEAR GUARANTEED WARRANTY IS SIMPLE!

TERMS:

From the date of your battery purchase through year number 10 of ownership, your battery is covered. If it stops working during this time, we will repair or replace it with a battery of equal or greater value for FREE!

SHIPPING:

We cover all shipping costs associated with shuttling your battery back and forth for repair or replacement. It is our warranty; it is our cost; not yours.

EXCLUSIONS:

There are NONE! You trusted Millertech®, and if it’s within the warranty period your Millertech® battery is completely covered for everything!

PROOF OF PURCHASE:

You don’t need one. If it’s Millertech®, it’s covered!

FOR WARRANTY SERVICE CALL: 855-MAX-LITH

EMAIL:  warranty@millertechenergy.com

Recommended Chargers

The Millertech 36V 50Ah Marine Deep Cycle lithium battery is engineered for a max charge voltage of 43.2V charging profile.

1) Millertech 36V 15A On-Board Lithium Battery Charger (3615M)

The Millertech 36V 15A On-Board Lithium Battery Charger is a waterproof lithium charger designed to mount permanently in your boat for convenient charging of 36V lithium batteries. 

Features and Benefits

• 15A output current for charging 36V lithium batteries. 

• 43.5V output voltage optimized for 36V lithium battery charging. 

• 110V AC input for standard shore-power outlets. 

• IP65 waterproof rating designed for marine environments. 

• Compact size: approximately 8″ × 5.5″ × 5″. 

• Lightweight design: about 4.8 lbs. 

Why choose it

• Built specifically to mount in boats for permanent installation. 

• Waterproof marine construction for harsh environments. 

• Compact and lightweight to save space on board. 

• Backed by Millertech’s 3-year guaranteed warranty with repair or replacement if it stops working during that time.

2) 12V-36V Dark Speed “On The Run” Dual Marine Charger

The Millertech Dark Speed On-The-Run Dual Marine Charger is designed to charge your lithium batteries while your boat is running by using the power from your engine’s alternator. This allows your trolling motor batteries and electronics batteries to recharge during the day instead of waiting until you return to shore power. 

Features and Benefits

• Dual charging outputs

  • Output 1: 14.5V – 15A (12V battery)

  • Output 2: 42.6V – 15A (36V battery) 

• Alternator-powered charging while running, allowing batteries to charge continuously while you are on the water. 

• Smart monitoring system prioritizes the starting battery before charging auxiliary batteries. 

• Automatic BMS wake-up function to activate lithium batteries that are in low-voltage protection mode. 

• IP65 waterproof rating for marine environments. 

• Built-in safety protections, including low-voltage, over-voltage, and overheating protection. 

Specifications

• Input Voltage: 90–130V AC

• AC Power Draw: 857W

• Start Transfer Voltage: 14V

• Stop Transfer Voltage: 13.3V

• Dimensions: 10¾″ × 7¾″ × 3½″

• Weight: 13.8 lbs 

Why choose it

• Recharges batteries while you are running the boat, maximizing trolling motor run time. 

• Eliminates the need for daily shore-power charging or generators. 

• Continuous charging throughout the day helps keep electronics and trolling motors powered longer. 

• Marine-grade waterproof design built for harsh boating environments. 

• 3-year Millertech warranty for repair or replacement if the charger fails during the warranty period.

3) Millertech 12V, 16V 36V, 3-Bank Battery Charger (Model#121636-3)

The Millertech 12V, 16V, 36V 3-Bank Battery Charger (Model 121636-3) is an onboard lithium charger designed to charge three separate batteries at the same time from one unit. It’s commonly used in marine setups where a boat has multiple batteries—such as a starting battery and an electronics battery. The charger is part of Millertech’s multi-bank lineup and is typically used when you want to charge multiple batteries overnight with a single plug-in connection.

This charger has three independent charging banks, each delivering about 15 amps, so each battery receives the proper charge without affecting the other. Because the banks are isolated, the charger automatically manages each battery individually to maintain proper charging and battery health.

Permanent Marine Installation. This is an onboard charger, meaning it is mounted permanently in the boat. After a day on the water you simply plug the boat into shore power and it charges everything automatically.

Why choose it

• Charge 12V, 16V, and 36V batteries with one charger.

• Ideal for boats running electronics, cranking batteries, and 36V trolling motors.

• Marine-grade durability for harsh environments.

• 3-year Millertech warranty for peace of mind.

Specs

• Input Voltage: 90–130V AC

• AC Power Draw: 1,340W

• Dimensions: 10.5″ × 9.75″ × 4″

• Weight: 15 lbs

This charger has three independent charging banks, allowing you to charge multiple batteries simultaneously without needing separate chargers. Each bank can be configured for different battery voltages:

• 12V battery bank – commonly used for electronics or starting batteries

• 16V battery bank – often used for high-performance marine electronics systems

• 36V battery bank – commonly used for trolling motor batteries

• Fully automatic operation – plug in and charge. 

• Marine-grade aluminum housing. 

• Waterproof cooling fan to improve heat dissipation. 

• LED charge indicators show battery status. 

• Lithium wake-up function for low-voltage protection batteries. 

• Built-in safety protections

  • Short circuit

  • Reverse polarity

  • Overcharge

  • Over-temperature