The most popular way to charge a 24-volt trolling motor battery system is with an onboard two bank battery charger like the Minn Kota Mk220d. Another option for charging your 24-volt battery bank is to use a 24-volt charger like the Samlex SEC-2425UL.
Note: most links in this article are Amazon.com Affiliate links, see Affiliate Disclosure, thank you.
How do I connect my charger?
There are two ways to connect a battery charger that depends on your charge voltage. I have two different voltage chargers on my boat (12-volt and 24-volts) and have drawn up a wiring schematic of my system. If you look over the schematic, you will see the chargers at the bottom of the image.
The charger on the left side of the image is a 24-volt charger. The 24-volt charger is connected to the negative on battery 1 and positive on battery 2, inputting 24 volts to the series battery bank. My 24-volt charger is a Samlex SEC-2425UL(link to Amazon.com)
The charger on the right side of the image is a 12 volt two bank or dual bank battery charger. The two bank charger is connected to each battery separately. The wires usually are color-coded to match your system, red is positive.
If either charger has a ground terminal, you must attach that to your boat ground in the same manner as your batteries.
What amp charger for deep cycle battery?
In a perfect world, you should use a charger that is rated just above 20% of the amp hour rating of your battery. On quality batteries, you can go up to 40% of the amp hour rating without damaging them, but some lower quality batteries will experience a drop in battery life. PennDeka recommends a 33% of amp hour rating on page 3 of its “basic rules for battery care” pdf (Dekabatteries.com, 2019) An example of a good size charger will be if you have a 100ah battery you would want to use a 25 amp battery charger.
When charging a flooded lead-acid battery, you should remove the caps beforehand and make sure the electrolyte covers the cells. After the charge cycle is complete, you should top the battery cells off to the fill line with distilled water.
Can I use a portable battery charger?
You can use a portable battery charger as long as the charger is rated to charge your batteries. A 24-volt system typically requires two 12 volt chargers.
For most deep cycle batteries, you will want a multi-stage smart charger. Most multi-stage chargers have three stages, charging, absorption, and float. As chargers get more advanced, they include more stages that include the ability to recondition your battery, which will extend your battery life.
Before you connect your chargers, you should disconnect your batteries from your electrical system completely to avoid battery or charger damage. Disconnecting and reconnecting your batteries can be a large amount of work if you fish often. I always recommend onboard battery chargers to avoid this extra work.
Most small portable chargers can cost far less than onboard chargers. Also, You can only charge one battery at a time, but you should let both batteries rest 24 hours before using them, so they have a chance to equalize.
Are onboard battery chargers worth the extra cost?
Onboard battery chargers are a huge time saver, and most are made just for this application.
Onboard battery charger gets placed in your boat where you can hardwire them to your batteries but still conveniently reach shore power with an extension cord. Most onboard battery chargers are designed for deep cycle batteries and run in multi-stages. My battery charger auto detects battery type, flooded, AGM, or gel.
There are many manufacturers of onboard chargers. Guest was the manufacturer of my first onboard two bank charger. My Guest 10 amp charger was a great charger and still works to this day, but I upgraded to the larger Minn Kota MK220D(link to Amazon.com).
The Minn Kota MK220D is a 20 amp charger that provides 10 amps to each battery. The MK220D takes about 7 hours to recharge my 100 ah batteries at 50% discharge.
Many people prefer to use 3 bank onboard charger for whole boat battery maintenance. A 3 bank onboard battery charger can connect to three batteries. One lead is connected to the main battery, and the other two leads are connected to the trolling motor batteries.
Are there other options for charging a 24 volt battery bank?
A 24-volt battery charger is an excellent option for a 24-volt battery bank. I have four batteries on my boat, two 24 volt banks that I call A and B.
I have a Samlex SEC-2425UL(link to Amazon.com) connected to my high amp-hour A battery bank. Samlex is a manufacturer of high-end chargers that produce a lot of different chargers for different applications.
When I talked to technical support at Samlex, they told me that a 24-volt charger was the only way to go for a 24-volt battery bank because it charges the batteries equally. The tech went on to explain that I will see a significant increase in the life span of my 24-volt battery bank because of the equalization.
Wiring A 24-volt charger into your system is easier to do and requires two fewer connections. The Samlex charger can fully recharge my 150 ah batteries at 50% discharge in just over four hours.
Promariner makes marine chargers in all sizes and all configurations. I don’t have personal experience with these chargers, but they are top-rated and have high customer reviews.
How do I charge my trolling motor batteries while on the lake?
How to charge a boat battery on the water can be difficult, but is doesn’t need to be. The best way to charge your batteries while on the lake is an alternator charger connected to your main motor.
How to charge a trolling motor battery from the outboard motor is simple using an alternator charger. Minn Kota makes a series of DC alternator chargers, and the MK-2-DC is a two bank model. The Minn Kota MK-2-DC(link to Amazon.com) is a 20 amp charger which can charge 10 amps per bank. When your main motor is running the charger comes on. I have to give the MK-2-DC a glowing review because I bought mine in 2011 and eight years later it is still working great.
The problem with DC alternator chargers is that when your motor is off, they can not charge your batteries. On long days fishing the bay, I have had to idle my main motor to get through the day, which is not good on your main motor.
A few hacks to charge your batteries while on the lake:
Solar panels are available in different voltages, sizes, and materials. I would buy a flexible 24-volt solar panel and attach it to the top of my boat. You cannot connect the solar panel to a battery bank while the charger is on because it can ruin the connections or wires. A solar panel would work great with my boat because my high amp battery bank B could be trickle charged all day.
Wind-powered generators are another option. Wind power is one of the easiest generators to install. Attaching a mounting bracket to your bow beck could get your turbine just above your boat top allowing you to generate power all day. The same rules apply with a single charging device to each battery bank as solar as to not damage the equipment or confuse the charge controller.
One downside to this device is that it could provide resistance making the trolling motor work harder, which will cause a net loss in power. The turbine I am going to buy on Amazon says it is rated for wind speeds of 147 miles per hour so I can run it while motoring provided I have a sound mounting system.
Generators have a variety of output connections available. It might be possible to find a 24-volt output generator. If you can’t find a 24-volt generator, you could plug in your charger when running on a different battery bank, but I would say to make sure you are grounded and don’t get it wet. Many generators run on propane, so you have little to no exhaust. Also, low decibel and compact size generators might be available.
Click here to read our review of Trolling Motor Batteries
Conclusion:
For a 24 volt battery bank, there is two way to charge your batteries. You can use a 24 volt charger or a 12 volt two bank charger. There are many options available to purchase, but I would stick with a marine option that is designed to be in wet environments.
As far as charging boat batteries on the water, test your system on land and always use the correct size fuse and proper gauge wires safety. Fires on boats are never a good thing, even if you have a bbq.
FAQ:
What is the correct size fuse to use on a 24-volt charging system?
Sizing your fuse correctly depends on two key factors, wire capacity, and your trolling motors maximum amp draw. First, you need to size your wire to match your trolling motor draw and length of wire using a chart that can be found at Minn Kota or your user manual. Then take the maximum amp draw add 8% ( x 1.08) and round up to the next size fuse. The most common size fuse for 24-volt trolling motors is a 60 amp. Note: most multi-bank chargers have fuses built-in.
The batteries are 24-volt, so what gauge wire should I use for my trolling motor?
Sizing your wire depends on the maximum amp draw of your motor and the length of your wire. Normally you can find a chart on the Minn Kota website or in your users manual, for an average size fishing boat the most common size is 6 gauge wire.
Tip: don’t hesitate to go up one size wire, spending extra money for quality wiring will save you money on every other part of your system.
Can you charge a 24 volt trolling motor system with a 12 volt charger?
A 12 volt charger can not charge a 24 volt trolling motor system. Your battery charger needs to work at a higher voltage than your battery bank’s resting voltage. For example, a standard 24 volt battery bank can have a resting voltage of 25.2 volts or higher. To charge a battery(or batteries) of this voltage, you should be in a volt range of 27 to 28 volts.
We recommend a 24 volt smart charger or a multi-bank 12 volt smart charger to get the best performance from your batteries.
Can you charge a 24V battery with a 12V solar panel?
A 12 volt solar panel can not charge a 24 volt battery. A typical 12 volt solar panel has an operating voltage of around 18 volt. This voltage goes into a charge controller that regulates it to charge a 12 volt battery. To charge a 24 volt battery, you need a 24 volt solar panel that outputs above 36 volts. This panel will feed a charge controller, like an MPPT, and send power to your battery until charged or the sunlight is gone.
Does a 24 volt trolling motor need 2 batteries?
A 24 volt trolling motor can use any number of batteries that adds up to 24 volts. Typically this setup will include two 12 volt batteries. When you connect two 12 volt batteries in series, you will have 24 volts at the same amp-hour rating as one battery rating. Some larger boats will use four 6 volt batteries because they are more energy-dense, but they add significant weight and require special wiring.
With the rise of lithium batteries is becoming more common to see one 24 volt battery. While the upfront cost is high, the benefits of life cycles, above 80% DOD, and weight make them great.
References:
Dekabatteries.com. (2019). [online] Available at: http://www.dekabatteries.com/assets/base/0004.pdf [Accessed 7 Jul. 2019].
