Does My Boat Motor Charge My Battery Or Batteries?


So, much of the world (or at least some of the world) already knows that a battery charges a motor engine. Much like a dog that bites a man is quite common knowledge and observation. But, a man biting a dog can provide for some strange entertainment. This is mostly because it is often taken as counterintuitive and maybe even taken as banal for a good number of people not used to it. While certainly not banal, charging a boat battery or batteries with a boat motor can certainly fit the bill of counterintuitive. It could work, for all we know, right? So, really, does my boat motor charge my battery? Does it work? Is it plausible? Well, for the love of science and all things related to boats and batteries, let us examine this proposition and situation.

When it comes to standard procedure, it is pretty much known to people that a battery is a heavily needed apparatus when it comes to making any vehicle move (there are exceptions, of course). By the same token, a battery will usually need some of the chargers into to keep on giving the energy to start an engine or sustaining energy throughout. This is especially true with the case of marine batteries.

In marine batteries, it is quite important for the two modes to be observed and respected. What are these two modes? Motors of marine batteries usually have (to current knowledge) a starting motor (what we know as cranking up the engine) and a trolling motor (for propelling later on bodies of water). Unfair as it can be (quite logical though) is that these two motors need two different batteries for each of these functions. These batteries, respectively, are cranking batteries and deep cycle batteries. Together, they work in tandem in order for a successful marine operation to be possible.

A car battery does not have a trolling motor and thus, does not need (again, to the given knowledge now) a deep cycle battery. These deep cycle batteries are responsible for downregulating and maintaining a steady stream (get it? Okay) of energy without burning out the motor. This is especially important in many marine operations, even at the small scale like bass boat fishing trips.

The reason this review is necessary is on the matter of design. It would not need the genius to realize that batteries are often design dependent and they exist to fill the function but within a given context. Working out methods to interchange their function may be a dream of scientist and experimenters all across the world, but it can often become a nightmare for standard manufacturers who just want to clearly delineate their products lines as this or that.

More importantly, as with specific design, these batteries (car or marine) have certain limits. This is especially true with the case of marine batteries (which serve two functions for a boat). Let us talk about battery safety and the potential (dangerous) problems that can befall a boat battery.

First off, as people may know, undercharging or overcharging can damage the battery really, really good. All right, we can get the logic behind overcharging a battery. We can probably understand that if we go full charge, something inside (in this case, electrolytes) that will boil over or burn out. This is will then cause a lot of damage to the protective layer (whatever it is) to a battery and will often lead to some kind of rust (mostly because of air).

This overcharging bias reaction is quite common to a lot of people. But undercharging is not a common thing you find when it comes to battery preservation. How could undercharge a battery cause it to be damaged? Well, turns out, this is mostly because marine batteries (like car batteries) usually contain lead-acid plates.

By virtue of its design, these lead-acid plates also contain a compound called sulfuric acid. The process of undercharging causes this compound to leak out and over time, causes them to accumulate within the plates and ultimately, bring about wear and tear from that point.

Even eery and creepy is the concept known to experts as sulfation (yep, it is a thing). Ever heard of gout? Gout is this medical diagnosis that is rampant across different populations around the world now. It is basically a disease when uric acid crystals (formed by meat and sugar) enter into the joints (commonly the legs) and crystallizes into a very painful block within that joint.

Well, it turns out, that sulfation is pretty much the same (minus the extreme, excruciating pain). The sulfur that leaks out eventually forms as crystals at the bottom. Again, this is caused by undercharging or discharging. Yep, due to light usage, this can often damage a battery. On the outside (like gout and a TV that does not turn on), it is all fine—no swelling. But, on the inside, damaged and rusty. Crazy stuff.

Be Quick About It! Answering The Question

Yes, it took a while to get to this point. But, safety and preservations of batteries are paramount.
All that said, there seem to be some methods that point to an outboard motor’s lightning coil as a viable option to charge a battery.

Peter Fildes seems to agree so. A lightning coil is found close to the flywheels of an outboard motor. These coils produce an alternating current (it can receive and redirect energy) and are often used to power small lights in small boats. As you can see, this alternating current of energy is only used to keep the light bulbs on.

Essentially, their power is halved from that point. So, according to Fildes, a “bridge” or “rectifier” is needed to access the maximized power current that these coils can potentially give. He sells a circuit that does just that.

But, in practice, you can give experimenting on building your own bridge and rectifiers on your own, too. Oh and also, the author points out that you will need a voltage regulator (to modulate energy) along with a “bridge rectifier”. Enjoy your experiments, folks!