Using the Alternator Charger

Alternator chargers put every ounce of power to good use. While on the water, they take your alternator's excess power and redistribute it to your trolling batteries. You get an extra boost, and better battery life.

The Alternator Charger does not need to be unplugged from the alternator on your outboard. It is designed to be permanently installed. The charger is only powered when connected to the ignition, the boat’s ignition key is turned to the "on" position and the battery connected to the alternator charger is above 13.6 Volts. The Minn Kota Alternator charger is designed to only begin charging trolling motor batteries after the starting battery has been fully charged. 

Using the Alternator Charger

  • The Alternator Charger will automatically start charging the trolling motor batteries once the starter battery reaches 13.6 volts and the ignition is on for the outboard motor. This prevents the starter battery from draining.
  • Each output bank is independent and isolated from one another. The Minn Kota charger can charge independent batteries or combinations of batteries hooked in series or parallel without disconnecting the batteries from any switches or wires / straps joining the batteries. See diagrams at the bottom of this page.

Minimum Input from the Outboard Alternator

In order to achieve full output, the minimum input to the Alternator Charger from the engine alternator should be:

  • MK 1DC - 12 amp minimum
  • MK 2DC - 25 amp minimum
  • MK 3DC - 35 amp minimum

Supported Battery Types

When the Alternator Charger is on and charging, it pushes 10 amps to the batteries to be charged until they reaches 14.4 volts. The charger will turn on when the starter battery is at 13.6 volts and the ignition is on for the outboard motor.

  • The Alternator Charger is supported for use with 12 volt Flooded Lead Acid batteries
  • The Alternator Charger is supported for use with 12 Volt Flooded AGM batteries
  • The Alternator Charger is not recommended for use with 12 Volt Gel batteries as they could be overcharged. The Alternator Charger charges the battery to 14.4 volts. Gel batteries should not be charged past 13.9 volts. If they are charged over 13.9 volts, the battery could be damaged. 
  • If you would like to use the charger with a lithium battery, we recommend checking with the battery manufacturer as lithium batteries have charging needs specific to the individual batteries.
  • When using the Alternator Charger, the starter battery should never be a lithium battery as the voltage will not drop below 13.6 volts and the charger will not turn off. This can cause the starter battery to be drained.

Mounting the Alternator Charger

Choosing a Mounting Location

When choosing a location for the Alternator Charger, you will want to keep the following in mind:

  • Do not mount the charger above batteries as lead-acid batteries give off corrosive gasses which will damage the charger over time. Never allow battery acid to drip on charger when reading electrolyte specific gravity or filling battery. Also, as with most electrical devices, do not mount the charger below the waterline of the boat or directly adjacent to fuel tanks.
  • Each DC input and output cord is 6 feet long. Make sure that all DC cords can reach the batteries.
  • If the DC battery leads are not long enough, they should be brought to a terminal block and extended from the terminal block with 12 AWG (minimum) wire. A fuse holder should always remain within 7 inches of the battery terminals. The maximum extension length is 15 feet. You may contact the Minn Kota Service Department with any questions.
  • Even though the Minn Kota charger is capable of operating in a high ambient temperature environment, a minimum of 6 inches of unobstructed area should be allowed on all sides of the unit for proper air circulation and cooling. Proper cooling and circulation will allow the charger to operate at peak efficiency.

Mounting the Charger

Due to the pounding that boats routinely endure, take the time to securely mount the charger to prevent damage. Mounting with bolts, nuts, and washers is preferable to mounting with screws. Use the largest diameter bolts possible, and use all four mounting holes.

CAUTION - Before making any connections to batteries in a confined space (such as a battery compartment of a boat), open the door or hatch of the compartment and allow it to air out for 15 minutes. This allows any gasses that have accumulated in the compartment to escape.


Connecting the Batteries to the Charger

  1. Find the input cable labeled “STARTING” and connect POSITIVE (RED) wire to POSITIVE (+) or ungrounded terminal on the starting battery. Then connect the NEGATIVE (BLACK) to the NEGATIVE (-) or grounded battery terminal on that battery.
  2. Find each output cable and connect POSITIVE (RED) wire to POSITIVE (+) or ungrounded terminal on the trolling battery. Then connect the NEGATIVE (BLACK) to the NEGATIVE (-) or grounded battery terminal on that battery.
  3. Connect additional output cables to additional batteries as described in step 2.
  4. For this DC Alternator Charger to function, find the purple ignition wire and connect it to the Ignition Circuit. This can be any +12v source that is only energized when the ignition key is turned on. Use the quick connect terminal provided. See diagram to the right. If the purple ignition wire is not long enough, it can be extended with 18 AWG wire.


Operating the Alternator Charger

Make sure the charger is properly mounted and the cords are connected properly to the batteries.
Double check the polarities of the cords and make sure the correct bank of the charger is connected
to the correct battery

LED Indicator Lights


The LED Indicator Lights show the state of the Alternator Charger. 

  • GREEN power LED: the ignitions is on.
  • RED power LED: the input cord to the starting battery is connected in reverse polarity.
  • YELLOW LED: The trolling motor battery(s) is(are) charging.
  • RED on the output: The battery is connected in reverse polarity.

Click here for additional information on the indicator lights and troubleshooting. 


The Alternator Charger needs occasional maintenance.

  •  Regularly check the charger for dirt, oil, battery corrosion etc. If you need to clean any corrosion, you can use a solution of water and baking soda and then wipe it clean with a dry cloth. 
  • Check ring terminals for dirt, oil, and battery corrosion; then disconnect from battery posts and clean as necessary with water and baking soda solution and dry with a clean cloth.


Battery Charger Manual

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