A boat that is idling will charge its battery, but it’s a slow process and not the best way to go about it.
You need higher RPMs, above idle around 2,000 before the alternator starts to put enough power back into the battery. Also, if the battery is so dead that it would not start the boat, then this is not the best option to charge your battery.
The best thing to do is hook up a smart battery charger (ad) and let it charge overnight. Stick to 2-amps of charging power or less and just let it sit overnight. You need a slow charge that is constant, and a battery charger is the only option, especially if the battery is fully dead. If you have large our dual batteries then 5-amp battery charger may be needed.
The number of battery charging amps affects charging speed, you don’t want too fast as you’ll cook the battery, so going lower and waiting longer is always the best.
The Alternator Is Not A Battery Charger
The alternator on a boat is made to supply just enough power to run things on your boat while the engine is on. It will charge a battery and keep it at a level it needs, but it’s not a battery charger.
The alternator is more of a battery maintainer than a battery charger.
It will not put enough power into a dead battery to get the boat running, it just supplies the needed power while running.
Using an alternator to charge your battery is a slow and unproductive process, so if your battery is dead, you should get smart battery charger.
What Is A Smart Battery Charger?
A smart battery charger is just like other 12-volt battery chargers, but it turns on and off as the battery needs it.
Dumb battery chargers used to be more common, it charged the battery, but you needed to be there to unplug it when it was one.
Then we got normal battery chargers that would turn off when the battery reached the correct charge level.
Now we can get smart battery chargers that turn off but also turn back on when it’s needed, with some even conditioning the charge to keep the battery active and happy when you’re not using the boat.
Ways To Keep Boat Battery Charged
It’s quite common for boat owners to get their boat ready for the season and see that the battery is dead.
Even if you keep the battery switch set to off, you can still find your battery dead. This is a greater problem for boats and jet skis that use smaller batteries.
It’s not the parasitic current draw that is the problem (which battery switches fix), but the fact that lead-acid batteries go flat if you don’t use them for months. The smaller the battery, the smaller the plates, and thus the more of a problem for batteries to die.
What you need is something that keeps the battery active when you’re not using it. A solar panel battery charger (ad) is the best option!
Stick to solar battery chargers that are 5-watts or less for your boat and keep it hooked up when you’re not riding. The solar charger will keep the battery active and happy and be ready when you don’t drive your boat for a while. If you go over 5-watts you’ll need a solar charge controller, this turns the solar charger on and off as it’s needed.
A charge controller (ad) is the best option if you want a “set it and forget it” even for 5-watt solar panels.
The solar charger is not a battery charger, it’s worse than using your alternator to charge a battery, but it’s more of a battery maintainer. If your battery is already charged and want to keep it that way, then a solar battery charger is what you need. It doesn’t even need to be in direct sunlight, just out in the open where some light can get to it, and it will help keep your battery active and happy for years.
How Long Do Boat Batteries Last?
Boat batteries will last for many years, but it all depends on how you use and maintain it.
If you take good care of your boat battery, it should last around 3 to 5 years without any major problems. However, if you fail to maintain your battery (like leaving the switch on when not in use) then you will find yourself having to buy a new battery much sooner.
Make sure you charge it when needed and use a solar charger if you don’t plan on using your boat for long periods of time. A good quality deep cycle lead-acid battery should last many years with proper maintenance and charging, but not taking care of the battery then getting one season out of it is not uncommon.