How Many Watt Solar Panel to Charge Deep Cycle Battery

Anthony Joseph Lalonde

Table of Contents

    How many watts of solar panel do I need to charge my battery? The short answer is that you will need a solar panel with a wattage rating that is higher than the total wattage rating of all the devices you want to power.

    For example, if you have a 100-watt TV and a 200-watt fridge, you will need a 300-watt solar panel. Of course, there are other factors to consider, such as the efficiency of the solar panel, the amount of sunlight available, and the capacity of the battery.

    In this article, we’ll take a closer look at how to calculate the number of watts you need from a solar panel to charge your deep cycle battery.

    What is a Deep Cycle Battery?

    Renogy Deep Cycle AGM Battery 12 Volt 100Ah, 3% Self-Discharge Rate, 2000A Max Discharge Current, Safe Charge Most Home Appliances for RV, Camping, Cabin, Marine and Off-Grid System, Maintenance-Free

    Unlike traditional lead-acid batteries, deep cycle batteries are designed to be regularly discharged and recharged. This makes them ideal for solar applications, where they are used to store energy collected during daylight hours for use at night or during periods of low sunlight.

    These batteries can be discharged to as low as 20% of their capacity without damaging reducing their lifespans by vast amounts, which means they can store more energy than traditional batteries and earning them the title of deep cycle batteries as they can withstand more extensive cycles of charging and discharging.

    They work in a similar way to traditional lead-acid batteries, however, the lead plates in deep cycle batteries are thicker so they can withstand more discharge and recharge cycles. Most automobiles do not run on them, but instead they are used for recreational vehicles, boats, and golf carts. These batteries are used in solar panels and other plug-in devices since they provide a consistent supply of electricity over an extended period.

    There are two main types of deep cycle batteries: flooded lead-acid (FLA) and sealed lead-acid (SLA). FLA batteries require regular maintenance, such as adding water to the cells, while SLA batteries are maintenance-free.

    Also Read: Best Deep Cycle Battery Charger

    How Do You Charge Batteries with Solar Panels?

    To charge a battery with solar panels, you will need a charge controller and inverter. This is an electronic device that regulates the flow of electricity from the solar panel to the battery, preventing the battery from being overcharged and an inverter is a device that converts the direct current (DC) power from the solar panel into alternating current (AC) power, which is the type of power used by most household appliances.

    The charge controller will also have a built-in diode that prevents electricity from flowing back from the battery to the solar panel during periods of darkness or low sunlight. You can use either a 12 volt or 24-volt solar panel to charge a 12-volt battery, but using a higher voltage panel will result in faster charging times. 

    You can use either a portable solar panel or a permanently installed one. If you are using a portable panel, you will need to connect it to the charge controller with cables. The system above is the simplest way to charge a battery with solar panels, but there are other methods that can be used if you want to increase the efficiency of your system.

    How Many Watts of Solar Panel to Charge Deep Cycle Battery?

    The following table is a guide on how many watts of solar panel you will need to charge a deep cycle battery with different capacities, voltages and hours needed of sunlight per day.

    AmperageSolar Panels wattage (watts)Time to charge (Hours)Amount of sunlight a day (Hours)Time to charge (Days)

    What Conditions Can Impact How Fast the Battery Charges?

    Here are the three main conditions that will impact how fast your solar panels can charge your battery: 

    Wattage of the Solar Panel

    The wattage of the solar panel is the amount of power it produces and it is rated in watts. The higher the wattage, the faster it will be able to charge your battery. Wattage is calculated by multiplying the volts by the amps. For example, a 100-watt solar panel produces 8.3 amps at 12 volts. 

    Do keep in mind that batteries are rated for maximum wattage output, so you cannot charge a battery any faster than its maximum rate. Most deep cycle batteries have a maximum charge rate of around 50 amps, which means you would need a solar panel with a wattage of at least 600 watts to charge it at its maximum rate.

    The Number of Batteries Being Charged

    Of course, the more batteries you are trying to charge, the longer it will take. If you are only charging one battery, it will obviously charge faster than if you were trying to charge three batteries.

    Connecting multiple batteries in parallel will increase the capacity but not the voltage, while connecting them in series will increase the voltage but not the capacity. The best way to charge multiple batteries is to connect them in both parallel and series so that you can charge multiple batteries at once while still getting a high voltage.

    Also Read: The Difference Between Batteries in Series vs Parallel

    Whether You Are Using Power In The RV at the Same Time

    The best way to charge your batteries is to disconnect them from the RV and any other devices that might be drawing power from them. This way, all of the power produced by the solar panels will go directly into charging the batteries. 

    However, if you are using power in the RV at the same time, this will obviously slow down the charging process because some of the power will be used to power the RV instead of going into the batteries.

    An RV camper is parked on the side of the road while charging a deep cycle battery.

    How Much Sunlight You Are Getting

    Most importantly, the amount of sunlight you are getting will have a big impact on how fast your batteries charge. More sunlight means more of the sun’s energy is being converted into electricity, which means the batteries will charge faster. 

    If you are in an area with a lot of cloud cover, this will obviously reduce the amount of sunlight that is reaching the solar panels and will slow down the charging process. So, make sure you are in a sunny location if you want your batteries to charge quickly.

    Will the Number of Solar Panels Decrease Charge Time?

    It is very common for people to assume that the more solar panels they have, the faster their batteries will charge. However, this is not always the case. 

    Remember, the maximum charge rate of most deep cycle batteries is around 50 amps. So, even if you have four 100-watt solar panels, that is still only 400 watts of power. Hence, you would not be able to charge the batteries any faster than if you had just one 100-watt solar panel. 

    Other ways to decrease charge time is by not using power while the batteries are charging, and by making sure you are in a sunny location.


    So, how many watts of solar panels do you need to charge a deep cycle battery? The answer depends on a few factors, including the wattage of the solar panel, the number of batteries being charged, whether you are using power at the same time, and how much sunlight you are getting. Keep these factors in mind when choosing a solar panel to charge your deep cycle battery.

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