Off-Season Battery Care
Published: Wednesday, November 9, 2022 12:00 pm
By: Dan Armitage
A version of this article appeared in the Buyer's Guide 2023 of Great Lakes Scuttlebutt magazine.
When electronic accessories aboard went south at the end of this past fishing season, I pulled the “house” deep-cycle battery out of my boat and had it tested. The four-year-old battery failed that test and explained why on the last couple of fishing trips I needed to place my battery selector switch on BOTH to draw power from the deep-cycle and the starting batteries to operate things such as my VHF radio, nav, underwater and courtesy lights, and my fish-finder. With the house battery dead, that meant the accessories were drawing only from my starting battery and put me in a potential position of unknowingly depleting that cranking cell and not having enough juice left to start the outboard when needed.
I dodged that bullet, but had to replace a $300 battery and question why my “state of the art” on-board charger allowed the premium AGM battery to die. The electrical pros who did the testing said it appeared that the battery had been overcharged by being topped off too many times when it wasn’t needed, and asked how often I charged it during the off season. When I responded that I left the smart charger plugged in and on most of the time, they said that was the culprit, adding that my smart charger should have recognized the problem and dealt with it internally.
That’s when I got in touch with my contact at Minn Kota and bounced the following questions off rep Adam Knowles:
What’s the difference between marine grade and automotive chargers?
“The obvious initial difference is going to be the shock and vibration resistance of a true marine rated product. Boats can be hard on equipment no matter what it is and our chargers are designed to hold up in places where many traditional or automotive chargers wouldn’t.
“The second big difference is that premium on-board chargers are designed to be safely left plugged in for longer periods of time through automatic multi-stage charging. By breaking the charge process into three distinct parts, we’re able to apply the right amount of current at the right time in the charging process. This includes the continued monitoring of the battery during the float or maintenance phase to prevent overcharging.”
Do you need separate chargers for different types of marine batteries?
“It is important to say that every battery and manufacturer is different and has different needs. The engineers at Minn Kota work with battery manufacturers directly to develop our charge curves in an attempt to cover as many rigging scenarios as possible. That being said, Minn Kota Precision chargers offer battery selection by bank – meaning if you want to use multiple battery chemistries in a single boating application you can program your charger to do just that.”
Shouldn’t premium chargers prevent over-charging?
“Absolutely. It is also important to note that float chargers are different from trickle chargers. A trickle battery charger will charge a battery at the same rate as the battery’s self-discharge, which is how quickly a battery’s capacity falls during storage. Many trickle chargers will output the same voltage and current regardless of the needs of the battery to reach 100% capacity, which can lead to battery damage if substantially overcharged. Minn Kota on-board chargers prevent overcharging by moving intelligently through the three stages of battery charging and monitoring and maintaining peak battery capacity during the Float phase.”
Can you leave an on-board charger on all winter/season?
“The first thing I recommend at the end of the season is to disconnect batteries from all the boat leads and label the wires with what battery they went to and what they power. You’ll be surprised how foreign your battery setup may look come spring, but disconnecting is a good practice to prevent parasitic draws on batteries over the off-season.
“Next, topping off the electrolyte of flooded lead-acid batteries with distilled water is a good practice to prevent corrosion on the topmost portion of your lead plates which can lead to diminished capacity.
“Last and maybe most importantly is to make sure the battery compartment is well ventilated. Off-gassing that occurs during charging can release hydrogen and other volatile gasses which can combust if exposed to a spark.
“If you follow these few guidelines and live in a climate that doesn’t have prolonged, extreme cold temperatures you should be able to start the season in the spring with batteries as fresh as you left them.”
Must you remove batteries from boats stored over the winter in freezing climates?
“It’s a good idea to pull batteries from boats that are stored outside in some of the more frigid areas of the country. This will prevent battery electrolyte from freezing or cases becoming brittle and cracking in more extreme climates.”
What features should you look for in a marine charger?
“The very first thing to ask is “how many batteries do I have any how much time do I usually have to charge them? Generally, the number of banks on your charger should match the number of batteries you have. The output per bank will determine how much time it takes to charge each battery. If you normally have longer times between outings a 6-amp output will most likely work for you, but if you find yourself staying out late and getting up early for multiple consecutive days a 15-amp charger will have your batteries back to a full charge much more quickly.
“After determining number of banks and output, at the bare minimum a good starting point would be a charger with multi-stage or ‘smart’ charging – this is what will allow you to keep batteries charged over long storage times. If you want to optimize for multiple different battery types, i.e., Flooded Lead-Acid, AGM, Lithium - a charger with battery selection by bank will do that for you.”
What is the most common cause of marine battery failure?
“Hands down the most common cause of marine battery failure that I see are batteries that haven’t been maintained properly. Storing discharged batteries over long periods of time and failure to top off electrolyte can cause premature failure of individual cells or entire batteries through the process of sulfation, or the corrosion of the internal lead plates of the battery. The truth is most batteries ‘fade away’ or simply fail to hold or take a charge vs. some type of more violent failure.”
Where can Great Lakes Scuttlebutt readers get more information?
“On our website we actually have a variety of blogs that help with understanding battery chemistries, how to select and charge certain batteries, and things as simple as rigging batteries in series or parallel if you’re new to rigging marine batteries. (www.minnkotamotors.com/blog/battery-chargers)”
After our conversation and poring over a couple of those blogs, I have a much better understanding of how best to keep my boat’s batteries at their peak, in-season and off.
tags: Batteries & Chargers, Education, Off Season
