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A boat's battery will charge while the boat is idling, but it's a slow process and not the best way to charge it. The alternator has to run all the electronics before charging the battery, so while idling, there isn't much extra power. The output current needed for a recharge depends on the rotational speed of the alternator. If the battery is entirely dead, idling won't be enough to charge it back up as it would take too long. Revving the engine will charge the battery faster as it means the crankshaft turns faster. However, this can be inefficient as you're wasting fuel. The best way to charge a boat battery is to take it out for a short period and give it bursts of power or use a smart battery charger.
| Characteristics | Values |
|---|---|
| Will a boat battery charge while idling? | Yes, but it is an inefficient way of charging the battery. |
| How does a boat battery charge? | The alternator uses the rotation of the engine to generate electricity inside its coils. This alternating current is then turned into a direct current to recharge the battery. |
| How long does it take to charge a boat battery by idling? | It depends on the boat and the type of battery it uses. It is not a very efficient way to charge a boat battery, and it might take hours to get a full charge. |
| Does revving the engine charge the battery faster? | Yes, revving the engine will charge the battery faster as it increases the rotational speed of the alternator. |
| How to know if a boat battery is charged? | A fully charged boat battery should measure at 12.6 volts or higher when not in use, and between 13.7 volts and 14.7 volts when the engine is running. |
What You'll Learn
Idling will charge a boat battery, but it's slow and inefficient
The alternator in a boat is designed to supply just enough power to run things while the engine is on. It will charge a battery, but only when there is power left over after running other electronics. This means that while idling, there isn't much extra power to charge the battery. The output current needed for a recharge depends on the rotational speed of the alternator, which is why higher RPMs are required for a substantial charge.
The battery will charge more efficiently when the engine is running at a certain RPM, where the alternator is rotating at a higher speed. The change in revs as you drive around naturally charges the battery in a better way than would happen by simply idling the boat.
If your boat battery is entirely dead, idling is far from an ideal way to charge it back up as it would take too long. You are better off taking the boat out for a short period and giving it bursts of power than letting it idle for long periods. Revving the engine charges the battery faster, as the crankshaft turns faster. This method works, but it can be inefficient as you are wasting fuel. It's better to take the boat out and naturally rev the engine while using it.
If you aren't planning on taking the boat out, the best way to charge a battery is by using a smart battery charger. This will ensure a slow charge that is constant, and a battery charger is the only option, especially if the battery is fully dead.
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Revving the engine will charge the battery faster
Revving the engine will charge a boat battery faster. This is because the crankshaft turns faster when the engine is revved, and the crankshaft is connected to a belt that runs the alternator in the boat. As a result, the faster rotation of the alternator produces more electricity, which recharges the battery quicker.
However, it is essential to note that revving the engine to charge a boat battery is not the most efficient method. While the battery will charge faster, this approach wastes fuel. It is more economical to take the boat out and let the engine rev at normal operating speeds.
Additionally, the output current required for recharging a boat battery depends on the rotational speed of the alternator. The alternator must first produce enough current to power the ignition, heater fan, and other accessories before it can charge the battery. Therefore, when the boat is idling, the alternator's output is primarily dedicated to running the boat's electronics, leaving little extra power for charging the battery.
If the boat battery is entirely dead, revving the engine may not be the best option for recharging it. In such cases, it is recommended to use a smart battery charger instead. A smart battery charger adjusts its output based on the battery's needs, turning on and off as required. This ensures a constant and slow charge, which is ideal for charging a dead boat battery.
It is also worth mentioning that revving a cold engine or an engine in neutral to charge the battery faster can potentially cause excessive engine wear due to sudden temperature spikes. Therefore, it is crucial to let the engine idle for a few minutes to warm up before revving it to avoid potential engine damage.
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A smart battery charger is a good alternative
Smart battery chargers, on the other hand, are designed to turn on and off as needed, maintaining an optimal charge without overcharging the battery. This is an improvement over traditional "dumb" battery chargers, which had to be manually unplugged once the battery was fully charged, and "normal" battery chargers, which only turn off when the battery reaches the correct charge level.
Smart battery chargers are also useful if you don't plan on using your boat for extended periods of time. They can hold the voltage at its prime level and reduce the current to almost zero, preventing overcharging even when the battery is left for months.
When choosing a smart battery charger, it is important to consider the number of amps. A higher number of amps will charge the battery faster, but too high of a setting will "cook" the battery. For most boat batteries, a setting of 2 amps or less is recommended. If you have large or dual batteries, you may need a 5-amp charger.
In addition to smart battery chargers, solar panel battery chargers are another option for keeping your boat battery charged when not in use. Solar chargers of 5 watts or less can be left hooked up to your boat when not in use, and they will keep the battery active without overcharging it.
- NOCO Genius GEN5X2, 2-Bank, 10A Smart Marine Battery Charger
- NOCO Genius GEN5X1, 1-Bank, 5A Smart Marine Battery Charger
- NOCO Genius GENPRO10X1, 1-Bank, 10A Smart Marine Battery Charger
- NOCO Genius GENPRO10X2, 2-Bank, 20A Smart Marine Battery Charger
- ProMariner 44021 ProSport HD Waterproof Marine Battery Charger, 20 Amp, 3 Bank
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Solar panel chargers are another option
Solar panel chargers for boat batteries are typically small, portable, and waterproof. They trickle charge your battery, maintaining its charge rather than delivering a large amount of power in a short time. This makes them perfect for keeping your battery charged when your boat is idle for long periods.
When choosing a solar panel charger, it's important to select one that is compatible with your boat battery's voltage, typically 12V. You can find solar panel chargers in a range of wattages, from 5W to 30W. A 5-watt solar panel charger is sufficient for most boats, and you can find options that include a charge controller, which turns the charger on and off as needed.
Some popular options for solar panel chargers include the POWOXI 7.5W charger, the SUNER POWER 12W charger with an MPPT charge controller, and the SOLPERK 20W solar panel kit with a controller and mount bracket.
Solar panel chargers are a great way to keep your boat battery charged without having to rely on idling your engine or using a smart battery charger. They are energy-efficient, cost-effective, and convenient, making them a popular choice for boat owners.
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A boat battery should be charged roughly after every 30 days of non-use
A boat's battery will charge while idling, but only a small amount. The alternator has to power all the boat's electronics before charging the battery, so there isn't much extra power. Therefore, it is inefficient to charge a boat battery by idling, and it will take a long time. If the battery is completely dead, it is better to take the boat out for a short period and give it bursts of power, or use a battery/smart charger.
If you are leaving your boat in the water, there is no need to remove the battery. However, you should get a smart charger to keep the battery charged. This is because the bilge pumps need to have power in case the water level rises inside the bilge. A smart battery charger will ensure the battery does not get overcharged, even when left for months.
To check if your boat battery is bad, you can physically examine it for any issues, such as broken terminals, leakage, discolouration, or cracks in the outer casing. You can also use a voltmeter to determine the state of charge of the battery. If the battery gives 0 volts as a reading, it is likely to be a short circuit. If the battery is fully charged but still below its maximum voltage output, this means the battery is probably sulfated.
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Frequently asked questions
Yes, a boat battery will charge while idling, but it is a slow and inefficient way of charging.
A boat battery is charged by the alternator, which is a generator driven by the belt from the engine. When the engine is running, the alternator uses this rotation to generate electricity inside its coils. This alternating current is then turned into a direct current to recharge the battery.
Idling your boat's engine will eventually charge the battery, but it will take a long time. It is recommended to take your boat out for bursts of power or short periods of normal operation to charge the battery more effectively.
Yes, revving the engine will charge the battery faster. This is because the crankshaft turns faster, which means the belt connected to the alternator also turns faster, producing more electricity. However, this is still an inefficient way to charge the battery as it wastes fuel.
You can use a voltmeter to check the voltage across the battery terminals. A fully charged boat battery should measure at 12.6 volts or higher when not in use, and between 13.7 volts and 14.7 volts when the engine is running.
