Techniques to Charging a Battery


Jumper cables isolated on white background
Jumper cables isolated on white background

I am not a fisherman by nature, so I had no idea what was happening when the boat we were on refused to start. It was only when my friend’s expression showed real frustration that I began to understand there was an issue.

I had never even heard of ‘trolling an engine’ – the only trolling I know of comes from story-books or Twitter. After we got off the lake where we had temporarily been stranded, I started to look into things and made an interesting discovery.

The issue with that particular boat was battery related; it had been improperly charged and left far too long without usage, two common issues that can wreak havoc on an otherwise pleasant boating experience. In actuality, the battery issues my friend’s boat suffered from are not uncommon – they are common issues among cars, as well.

How can someone take proper car of a motors battery? Here are a few pointers.

Choosing the right trolling battery

What are some of the common elements someone should look for in a trolling battery? Your deep-cycle (trolling) battery should offer these basic features:

  • Should be 12-watts
  • Should offer low current for long durations
  • Should be compact and under 50 pounds

There are quite a few websites that offer ‘best batteries for trolling’ reviews:, SaltyDogsGuide, FishingTipsDepot and the ever popular

These sites can help you prepare to find a battery, but how should you charge it once purchased? There are a few simple steps that can help safely and effectively keep your trolling motor’s battery in great shape.

Charging your trolling motor’s battery

Once upon a time, boat batteries were re-charged by literally pouring battery acid into a battery container. These days, that sort of effort is no longer necessary thanks to some serious advancements in electrical discharge technologies.

The biggest reason a comprehensive listing of batteries precedes the manner in which to best recharge them is simple: there are numerous different types of batteries, and they all require slightly different battery charging techniques. There is even variation in the type of charger you can use, be it a portable recharging system or a hard-wired recharging system.

Each of these battery systems will require their own charging methods, but the biggest distinction is between flooded cell (old-school), sealed ‘Gel’ batteries and AGM, or sealed / gel battery systems of modern construction, built in a slightly different way than Gel batteries.

  • Gel batteries: These batteries use regular acid, but a thickening agent prevents any of the acid from leaking. They will work even if there is a crack in the battery case. They cannot be refilled, so monitoring the charge is essential.
  • AGM: Spill-proof batteries are easily charged, but avoid letting them get too low on juice; once dead, they are difficult to revive. AGM batteries can be quickly ruined if they are over-charged, so monitor their charging cycles carefully!
  • Flooded Cell: These old-school, ‘deep-cycle’ batteries are fed with actual battery acid to keep charged. Place a “negative plate” on the battery to create electrical reactions in the ions of the acid. Do not get the acid on you; it will burn!

Though there is some variance between the separate battery manufacturers, the basic principles of battery charging is to either hook a battery up to an electric charger or re-fill the acid inside.

How to quickly charge your deep cycle battery

The oldest battery technology features the deep-cycle batteries, described above. The quickest way to charge these batteries is to literally fill them.

There is an added danger, however. Whereas Gel and AGM batteries have a ‘risk’ of being ruined – rendered inoperable or with a substantial decrease from optimal performance – a deep-cycle battery can cause actual harm.

The acid can be dangerous, obviously, but so can mixing the acid and seawater. Seawater, if it gets into the battery acid, can create chlorine gas, which is not something you want to be ingesting while out on the high seas.

Do not charge your deep-cycle batteries too quickly, in other words, or you might make a mistake that could have dire health consequences. Otherwise, focus on having substitute materials and repopulate the acid stocks to quickly recharge your deep-cycle batteries.

As far as technical charging, deep-cycle batteries are charged by connecting a “negative plate” to the battery. This plate sends electrical signals through the acid, which charges the ions in the acid; this is what charges the battery.

A 10amp charger would take about 11 hours to charge a deep-cycle battery, on average. A smart-charger, or a charger with enhanced technology features, would probably charge at variable amps to improve the charging time dramatically.

Using newer technologies is the fastest way to recharge a battery. Many newer chargers are designed to dynamically regulate charge to efficiently recharge the batteries, but also to decrease the charge as the battery gets closer to full charge, and for a very good reason…

How to charge your boiling hot batteries

If your deep-cycle battery is really hot, or even boiling, you need to disconnect the charging system immediately. Remove the negative plate as soon as you can and keep a moderate distance away from the battery for a while.

With a boiling deep-cycle battery, there are only two viable options.

First, you can test the battery yourself by connecting it to a voltage meter and seeing if the 12V (for example) battery is producing 12V of electricity. For those a little less inclined to DIY with a battery test, you can also take it to a qualified battery shop, or mechanic with experience dealing with batteries.

Unfortunately, if the acid has gotten hot enough to boil, the chemical composition of the acid is unlikely to retain its optimal performance levels. The boiling will create a chemical reaction that reduces the battery charge substantially.

As such, any deep-cycle battery that has boiled would be effectively limited, if not ruined, for future uses. A replacement is likely necessary.


Boating batteries are not necessarily complicated, but using them properly to get the best out of them can be a difficult task. Using the right tools with the right knowledge is important.

This review was just that: a review. This information is bare-bones to give you an idea of what you are working with, and what you should look for, but it is by no means a comprehensive step-by-step guideline on what you need to do to keep your batteries in the best shape possible.

If you are unwilling to learn the secrets of amp levels, voltage meters and similarly complicated engineering concepts, however, perhaps getting a smart charger and keeping an eye on a charging battery will be enough to keep the electric on in your boat?

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