One upgrade RVers and boaters often make is to their battery systems. Whether you’re adding an additional battery or a whole new solar power system, choosing the correct battery cable size for your system is critical. Let’s jump in and talk about why it’s so important to select the right cable size and, more importantly, how to do it!
Cables coming directly from your battery are the main artery of your RV electrical system. Since they come directly from the battery, they typically carry more current (measured in amps) than any other cables or wires in your RV. As a result, your battery cable size will need to be rated for the highest current and ultimately the thickest.
What size wire you need for your battery cabling depends on how much power your RV requires. There isn’t one correct answer to this question.
Below we will discuss how to figure out how much power your RV uses and how to use that information to select the proper cable size for your batteries.
Wire gauge is the measurement of a wire’s diameter or thickness. The US standard for measuring wire gauges is the American Wire Gauge scale, or AWG for short.
In the AWG system, the higher the number of the cable rating, the thinner the wire and, therefore, the less current it can carry.
For example, if you look at the chart below, you will see that 12 AWG, which has a diameter of 2.05 mm, can carry 20-25 amps up to 4 feet. 14 AWG, which has a diameter of 1.62 mm, can only carry 15-20 amps the same distance.
Thicker wires can carry more current for longer distances. Without getting into the math behind it, the reason for this is that a cable’s resistance increases as its diameter decreases or the length increases.
Therefore, the size cable you need depends on two things: how much current you need to carry and how long your cable runs need to be. This is why the AWG sizing chart lists the different current capacities at various lengths. As the cable length increases, so does the required cable thickness.
Wires have a maximum voltage rating as well. However, since your RV battery cables will only be 12 volts, you do not need to worry about the voltage rating when determining which battery cable size to use.
As we mentioned earlier, thicker wires have lower resistance. Resistance in a wire causes two main things to happen as current passes through it.
The first is that a voltage drop occurs. This means that the voltage at the end of the wire is lower than the voltage at the battery. If you have too much drop in voltage, your electronics will not work.
The voltage drop in a wire is calculated using Ohm’s law, V=I*R. V is voltage drop, I is the current passing through the wire, and R is the wire’s resistance. As you can see, if you increase the current, the resistance, or both, you will increase your voltage drop.
Resistance in a wire is dependent on both the thickness (the gauge) and the total length of the wire. If you undersize your battery cables, one issue that can occur is an excessive voltage drop that may prevent your electronics from working.
The second thing that happens as current passes through a wire is that heat is generated. Much like voltage drop, more resistance in the wire results in more heat being generated. If wires are undersized, they can get so hot that the casing melts and can cause a fire. Fires are much more catastrophic than too much voltage drop and are the main risk in choosing too small of a battery cable.
RV fires often lead to the complete loss of not only the RV but also its contents. Having wire that is overrated for the amperage helps protect wires from overheating and potentially igniting. While it’s better to be safe than sorry when it comes to wire gauge, going too big has some drawbacks as well.
There are three main drawbacks to choosing a battery cable wire gauge that is too big: cost, weight, and ease of use.
Probably the most significant consideration is cost. Thicker wire gauges cost more. If you are only running a few feet of battery cable, the additional cost will be insignificant. As cable runs get longer, cost becomes more of a consideration.
Similar to cost, as the wire gauge increases, so does the weight. Again, if your cable runs are short, the added weight will be negligible.
The last drawback to using thicker cable is that working with it is more challenging. Trying to bend and manipulate overly thick cabling in an RV’s small cramped compartments is not a fun time.
The drawbacks to oversizing your battery cabling are much less risky than choosing cables that are too small. However, choosing excessively thick cables can add unnecessary cost, weight, and frustration to your project. While it’s smarter and safer to choose too big rather than too small, just picking the thickest cable you can find isn’t a great strategy either.
Calculating your current requirements is pretty straightforward. Most appliances and electronics in your RV will have a current and power rating. If all of your electronics run on 12 volts (the same as your battery system), you simply add up the current ratings for each to determine your total current draw.
If you have appliances and electronics that run on 120 volts, the same as the power available in your home, you will need an inverter. An inverter converts DC power (from the battery) to AC power (like in your house). The process for calculating your current requirements with an inverter is simple as well.
You first need to add up the total power requirements (in watts) of each appliance in your RV to determine what size inverter you need. For example, if the combined power requirement of all your appliances and electronics is 2,500 watts, you probably want a 3,000-watt inverter.
Once you know your inverter size, the calculation to figure out the current draw is easy. Simply divide the watt rating of the inverter by the input battery voltage. In our example above, you divide 3,000 watts (the inverter rating) by 12 volts (the battery voltage), giving you a maximum current draw of 250 amps.
Remember that choosing the correct wire gauge for your battery cable size is based on two factors: current and distance.
Now that you know how to calculate your current requirement, you just need to figure out how far you need to run your cables. Remember, shorter is always better. Less cable means less weight and lower cost.
After you know both the cable length and the current, you can quickly look up what size battery cable to use. The wire sizing chart below helps you choose the correct wire gauge for your RV batteries. From this table, it’s easy to see that lower current and shorter distance allow for smaller cables.
You’ll also see that as current or distance increases so does the required cable thickness. Reach out to an expert if something becomes confusing; guessing which wire gauge is not the solution to your problem.
RV battery cables are a small but essential part of a complex and integral system in your RV. Choosing the wrong size battery cable can lead to extra cost, frustration, and potentially even a fire.
However, picking the correct battery cable size for your system doesn’t need to be stressful. Use the tips above or reach out to a Battle Born expert with any questions to help make your RV battery upgrade project a success!
We know that building or upgrading an electrical system can be overwhelming, so we’re here to help. Our Reno, Nevada-based sales and customer service team is standing by at (855) 292-2831 to take your questions!
Also, join us on Facebook, Instagram, and YouTube to learn more about how lithium battery systems can power your lifestyle, see how others have built their systems, and gain the confidence to get out there and stay out there.
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18 thoughts on “What Battery Cable Size Should I Use?”
In the above wire gauge table you refer to โcable lengthโ. Is this a two conductor cable?
If so, please confirm the table accounts for the total resistance (current running to and from the load) vs running a single conductor with local ground?
Hi Bill, thanks for reaching out and I apologize for the delay in getting back to you. If you give our sales and tech team a call at 855-292-2831 we certainly can help with any wiring assistance that you may need.
I am going to run two 12 v batteries to my camp trailer the cables that are on the trailer are two guage can I use 4 guage for the cross over from one battery to the other?
Hi Jesse! Thanks for reaching out. Our team notes that 4 gauge is too skinny of a wire and the skinniest you can use is 1/0. If you’d like additional information or assistance please give our sales and tech team a call at 855-292-2831 and they’ll be ready and willing to help.
Hi, I am looking for the correct wire size for 400ah battery string at 12v. Hoping you can help. By the way we are loving the batteries and adding two more. Thanks in advance.
Good morning Philip, thank you for reaching out. Our team suggests that 2/0 is a good wire size for your current system, and it works if you have plans to grow the system in the future. Please let us know if you have any additional questions.
I am preparing to replace a 2000 watt inverter/converter on my RV. In preparation I am looking at needing to add ring lugs to the 12 volt cables currently secured by set screws in the existing inverter/converter. The cable diameter with insulation is about 5/8″. Is that equivalent to 4/0 cable? Can I use ring lugs that attach with set screws rather than trying to crimp on in the limited space available?
Good morning Dave! This is a great question. Our team suggests that 4/0 should be fine but please note that our batteries ship with 18-8 stainless steel 5/16 โ 18 1โ and 1 ยผโ bolts, brass washers, and 18-8 stainless steel nuts with nylok inserts. If you have a bank of under 6 batteries, we suggest using 2/0 cable, but if you have 6 or more then 4/0 will work great. If you have any other questions about the install, please give our team a call at 855-292-2831.
Hi, I have a van conversion I am building. I have 1 205w solar panel, 1 100ah lipoe4 battery,a small 500w inverter. I will power a maxair fan, 12v compressor fridge and a few led lights. Everything is within 2 fet of battery. Will 4awg cable be ok?
Hi Mike, I apologize in the delay in getting back to you. Please give our technical sales team a call at 855-292-2831 and they will be able to assist with any issues you may be experiencing in your van build.
Having 12 volt in my motor home. 8 house batteries one year old. When installed, I question the installer about the size of the wires between batteries(new wires). They are a lot smaller than previous ones. Have been hooked up to 50 amp service for this year. Iโve been having 12 volt problems during this time, fans working some times, not others. Could these smaller red wires be a part of the problem? It seems that the batteries discharge fast when the power goes off between that and the time it takes to start the generator.
Hi Ron. It is possible that the smaller cables could be part of the problem causing your fans to not work at times. One issue that can occur when battery cables are too small is an excessive voltage drop that may prevent electronics from working.
Hello. I am upgrading my house bank to four 105 amp/hr batteries, 420 amp/hrs total. My wire run is 12 ft one way , from the batteries through the battery switch and then to my main DC panel. I have calculated my total required DC load for the boat to be 200 amp/ hrs.
What size wire do I require to connect the batteries in parallel and the wire size from the batteries to the main panel?
I will be connecting 3 170ah batteries in parallel, what cable would be best to connect the batteries to each other? Is 2/0 okay?
I have a 3000 watt pure sine inverter and max load I’ll ever have is about 3000watts @ 120v and only 600 watts @ 12v.
HiโฆI have a composting toilet that has a fan in it. I would like to connect it to a 12 volt battery. What size gauge do I need. It will run about 15 ft from fan to battery. Thanks for any feedback .
Hi Barb! The gauge wire size you need can be determined by first finding out the current rating (A) of the fan. Then locate that current rating on the chart above that corresponds to the column for a 15ft wire.
I have a rv that plugs into a 50 amp shore line a 2000 wt inverter and only 1 12 v battery I am replacing that battery with 2 100 ah 12 v batteries from yโall. What gauge jumper wire should I have made to connect the 2 batteries in parallel?
Hi Mark! Check out this blog to learn more about how to determine the right cable size for your batteries, https://battlebornbatteries.com/battery-cable-size/. If you have further questions, our technical sales team can help you at (855) 292-2831 (M-F 8:00am -4:30pm (PST).