Charging deep-cycle batteries must be done with a deep-cycle battery charger. These types of chargers are electronically controlled to supply the battery with a series of "steps" for charging. A regular battery charger is not equipped to handle the special needs of deep-cycle battery charging. Using a regular battery charger can shorten the life expectancy of a deep-cycle battery. Many marine-type, deep-cycle battery chargers are available. Some of these chargers can be permanently installed to the batteries for marine applications.
Identify the size of the batteries that are powering the trolling motor. In most applications the batteries are 12-volt. Some trolling motors may use a bank of batteries that are in a series connection. The total voltage for some of these applications may be 24 volts or even 36 volts. Choose the battery charger that best fits the voltage needs of the trolling motor's battery system by consulting the trolling motor specifications.
Mount the battery charger in accordance to the manufacturer's instructions. Many of the marine deep-cycle battery chargers are completely waterproof and can be located anywhere on a boat. These chargers come equipped with a set of electrical mounting rings that can be directly attached to the battery terminals.
Connect the positive (+) red cable of the battery charger to the positive terminal on the battery or the bank of batteries. Ensure that the connection is clean, tight and free of any debris.
Attach the negative (-) black cable of the battery charger to the negative terminal on the battery or battery bank. Again make sure the connection is clean and tight.
Plug the power supply cord into a grounded 120 VAC outlet. The charger should now be on. In most applications the charger will have two LED lights on its face. The green LED indicates that the 120 VAC power is going to the unit. The red LED signifies that power is being sent to the batteries.
Consult the battery charger's specifications if for some reason you receive a red blinking LED. This indicates that there is a problem with either the batteries or the charger. Various manufacturers will have different blinking codes for the red LED. When the red LED goes out and the green LED is still illuminated, this indicates the batteries are fully charged. The charger is still trickle-charging the batteries, while the green LED is on. There is no danger of overcharging the deep-cycle batteries using the proper charging unit.
- Charge batteries only in a well-ventilated area. Charging batteries emit flammable gas and can be highly explosive.
- Keep all batteries away from open flames.
- Follow all specifications on the battery charger as to temporary or permanent installation directions.