As most anglers know, marine batteries are a substantial investment. They’re powerful, long-lasting, and durable. But as in most things in life, you get what you pay for--and you pay a lot for batteries that can start your outboard, run your livewell and electronics, and keep your trolling motor humming-away all day long.
To get the most from your batteries, you need to take care of them. And though battery tech has improved a lot over the last two decades, reducing maintenance, they still need proper care to deliver the performance you paid for.
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We’ve discussed onboard chargers before, and if you need the full run-down, check out that article.
I can’t think of a more unappreciated--but important--piece of electronics. Anglers rely on their batteries for nearly everything we do, and the humble charger keeps them working like a charm as long as we do the minimum.
When selecting a charger, I recommend sticking to name brands. The work they do is simply essential, and saving a few bucks just isn’t worth it.
The most important considerations are matching the charger’s banks to your needs, getting the recharging times you want, and making sure that the charger you select can take the best care of the batteries you run.
Check out our buying guide for the best marine batteries available today!
This term can be confusing because it’s used by anglers in two different ways. A “bank” of batteries is a group of connected batteries–say, three 12v batteries running a 36v trolling motor.
But when talking about chargers, a “bank” is a single battery.
Chargers are commonly offered in 1, 2, 3, and 4 bank models.
You should select a charger with a number of banks that matches your total number of batteries, including your starting battery.
The deeper you discharge your batteries, the longer they’ll take to recharge. But another important factor governing recovery time is the amperage rating–per bank–of your charger.
Simply put, the higher the amps, the faster the recharging–all other things being equal.
If you’re a recreational angler who makes a trip or two a month, a slow recovery time might be just fine for you. But a tournament angler who needs a quick turnaround needs a much more powerful recharger.
Not all chargers are designed for more advanced battery types like gel, AGM, and lithium-ion.
Digital – Digital chargers are often compatible with AGM and gel batteries, as well as older flooded-cell tech. But they can’t be customized for different battery types, for instance, if you’re running a wet-cell starter battery and a three-bank set of AGMs for your trolling motor.
Precision – Precision chargers cost a bit more than their digital alternatives, but they allow you to select the battery type for each bank, ensuring maximum performance and battery life.
Lithium-Ion – Lithium-ion batteries require specialized chargers, and if you’re running one or more of these high-tech batteries, it’s best to contact the manufacturer for recommendations.
While it’s OK to mix and match battery types across applications, you should never mix them in tandem.
If you want to run a flooded cell battery to start your outboard, and a series of AGMs for your 36v trolling motor--that’s just fine. But you should never mix battery types within applications--for instance, two AGMs and one flooded cell in that 36v system.
Not only will that cause serious issues with charging, but it’ll also lower performance and may shorten battery life, too.
And in general, it’s always advisable to replace batteries at the same time. Mixing old and new will quickly degrade the performance of your replacement.
Flooded cell batteries--even the deep-cycle options for marine use--don’t tolerate deep discharges as well as AGMs. That’s a simple fact.
Repeated deep discharges cause the formation of large sulfate crystals. As Battery University explains, “During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the battery’s active material, which is responsible for the performance.”
Essentially, these sulfates eat the lead plates that are essential to performance.
And the longer your batteries remain deeply discharged, the more sulfates develop. That’s why it’s essential that you recharge every time you discharge.
Some chargers have a setting that’s designed to prevent and reverse sulfate damage, and these are always a good investment if you run flooded cell batteries.
Perhaps the chief enemy of battery life and performance are temperature extremes, and while marine batteries are built tough, extreme heat and cold are punishing.
Understanding the effects of heat and cold is critical for performance.
When the mercury rises, battery life is shortened, leading to unexpected--and sudden--failures. Indeed, standard lead acid (flooded cell) batteries are very sensitive to high summer temps.
As Odyssey Battery explains, “As lead acid batteries absorb high heat, chemical activity in the battery accelerates. This reduces service life at a rate of 50% for every 18°F (10°C) increase from 77°F (25°C). If a battery has a design life of six years at 77°F (25°C), and the battery spent its life at 95°F (35°C), then its delivered service life would be three years. This dramatic reduction in delivered service life can cause older batteries to suddenly fail in high heat because the accelerated failure rate occurs without warning.”
Worse still, “high heat will dramatically accelerate self-discharge rates, causing low states of charge, developing sulfation that will reduce performance and service life.”
I recommend that you check the water level in your flooded batteries every time you take your boat out in the heat. In an emergency, you can add simple tap or bottled water to refill your battery, but most manufacturers recommend distilled or deionized water to avoid impurities that can build-up in your battery.
Due to a very different chemical process, AGM batteries can stand the heat. And if you live where summers can feel like an oven, it’s probably wise to fork up the extra cash for these.
Whatever your choice, keep a close eye on the battery’s charge, invest in a top-end onboard charger, and keep track of the purchase date and expected service life of the options you go with. And if you’re in the market for an onboard charger, always choose one with an integrated temperature sensor to ensure proper charging.
Freezing temperatures really test your battery’s power output and ability to charge.
That’s because the chemical reaction that fuels your batteries is slowed down as the mercury plummets, and on icy mornings and raw afternoon, that can lead to a sluggish starting battery, slow recharging, and decreased run times.
The best defense against these problems is a solid onboard charger.
Temperature extremes are problems on the water, but they’re just as important to consider for storage.
Always store your batteries in a dry, temperature-controlled environment like your garage. It’s fine to leave them directly on the concrete--modern battery tech can handle that. But investing in a trickle charger to keep them in top shape over the winter is a very good idea.
If you run a boat that can fit in your garage, it’s fine to leave the batteries in place. But again, checking them regularly, keeping the fluid levels of flooded batteries where they should be, and attaching them to a trickle charger will prolong their service life and help them give you the most performance come spring.
Check out our top choices for the best marine battery boxes
Finally, it’s a good idea to periodically check and clean the terminals on your batteries. A simple stiff-wire brush will get the job done.
To get the most from your expensive batteries, you need to maintain them properly.
Take care of them, and they’ll take care of you!
Related: Marine Battery Group Sizes Explained