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My solar controller has a read-out of the voltage of my battery. Here it is a very safe 13.6 volts

My solar controller has a read-out of the voltage of my battery. Here it is a very safe 13.6 volts

You’ve made the decision to start a new, greener, happier life by giving up your house or apartment and moving into your vehicle. But wait a minute, what will you do for power?

  • What will you do for lights?
  • How will you recharge your laptop or camera?
  • How will you watch TV or DVDs?
  • In the heat of the summer, how will you run a fan?
  • In the cool of the winter, how can you power a 12 volt blanket?
  • What if you want a microwave?

These are pretty important questions. If you don’t think electricity is important, turn off the main breaker to your house and do without it for a week. After living in my van for a week without power, I knew I had to have it. I like to watch TV and DVDs. I want to be connected to the web via my laptop. I like the convenience of a microwave. So I found a way to have electricity in my box van. There are several ways to do this. We’ll start with the easiest, cheapest, and simplest and move onto the more expensive and difficult.

1) Use the car starting battery. While this works, it is not a good idea. You just use the starting battery of your car to run your “house” needs. Your car probably has a cigarette lighter. Since many 12 volt items come with a plug that goes into the cigarette lighter all you have to do is plug it in and it is running off your car battery. For example, many stores sell 12 volt, nine inch TV/VCR combos. For lights the simplest thing is to look around for a 12 volt trouble light at an auto parts store. I have bought them with a cigarette lighter plug-in or with alligator clips to clip on the battery. They have 50 watt bulbs which draw too much power so I replaced mine with 12 volt compact florescent I bought off eBay, or they are available on the web, just do a Goggle search. They put out the same amount of light but only draw 13 watts. For 110 volt items, you can buy something called an inverter. This allows your 110 volt items to be powered by your car’s 12 volt battery. They can be bought for about $40 at Wal-Mart. You plug the inverter into your cigarette lighter and then plug your laptop, TV, or battery charger into it. This works fine as long as you are driving, or running your car often. The problem is that the starting battery in a car is not designed to be discharged and recharged. It should be left nearly full all the time, otherwise it will lose its ability to hold any charge. So if you are parked overnight watching a couple of movies and running your laptop, the next morning your battery will probably be dead and your car won’t start. Very inconvenient! Do that a few times and you will be buying a new battery. Very expensive! While this is cheap and easy, it is also the riskiest way to get power. There are better ways.

2) Buy a Backup Battery Jumper. These are small self-contained batteries with attached jumper cables. They are intended to be carried with you in your trunk to jump-start your car if your battery dies. You can buy them with built in tire inflaters, lights, and even inverters to run 110 volt items. Nearly all come with an outlet to allow you to plug cigarette lighter items in. Make sure you get one that can be charged from your car’s cigarette lighter so you can recharge it while you drive. These have the advantage of providing you with power, and they won’t leave you stranded with a dead battery. Sam’s Club sells one for about $45. However, the batteries in these are not very good. They are small, will run down quickly with use, and will fail after a few discharges and recharges. So they really aren’t a good answer either.

3) Install a second deep cycle battery. This solution is by the far the best, so we’ll spend a lot of time explaining how to do it. First, let’s talk about which battery to buy and where to carry it, then we will look at how to keep it charged:

  • Which Battery to Buy: We need a deep cycle battery because they are designed to be discharged and charged hundreds, even thousands of times without harm to the battery. Also they have a much larger capacity. The capacity of deep cycle batteries is measured in amp hours (Ah). Let’s look at an example. You have a 9 inch TV that draws 50 watts of power and a light bulb burning that also draws 50 watts of power, so you are using 100 watts of electricity. To determine amps you divide watts by volts, so we have 100 divided by 12, which is about 8 amps. So every hour we draw 8.3 amps. Wal-Mart sells a 105 Ah battery for about $85. You might think that means you can run your TV and light for 12 hours, but it doesn’t work that way. Deep cycle batteries should not be run down beyond 50% of their capacity or they will be damaged. So our cheap Wal-Mart battery only gives us 55Ah of power, or about 7 hours for our TV/light combo. I have something called an 8D battery in my camper. I bought it at Sam’s Club for $116 and it has 225 Ah of capacity. At some point I will add a second one wired to the first giving me a total of 450 Ah of life. Then I could run our TV/light combo for 27 hours. Remember I said I replaced my regular 50 watt bulb with a 13 watt compact fluorescent? Let’s do the math with it instead. 50 watts and 13 watts total 63 watts, divided by 12 means I am drawing 5.2 amps instead of 8.3. So my two 8D batteries will run the TV/light combo for 43 hours. That one change gave me another 16 hours of use. Conservation is very important to us car/van/RV dwellers. I would probably use the lights and TV no more than 4 hours a day, so I could go 11 days without recharging the batteries. So we want to buy a battery with the largest capacity in amp hours we can, right? Not necessarily. The more capacity a battery has the larger and heavier it is. My 8D is about one foot across and two feet long. It weighs 130 lbs. It’s all I can do to pick it up into the camper. It’s a great deal, but if you don’t have room and can’t move it, it’s not a good choice for you.
  • How much will it cost? You can buy a cheap deep cycle battery at Wal-Mart for $65, or you can pay $300 for a Trojan, gel cell or AGM battery. If you only have $65 then your decision is made, you can’t beat the Wal-Mart price. For just a little more Sam’s Club sells 6 volt golf cart batteries for $80 each. You need to buy 2 and wire them together to make them 12 volt. Wired together they have 110 Ah capacity. So why are they better than the Wal-Mart battery, it has nearly the capacity and costs less? The first few years they would be just as good. But after that the difference in quality will become obvious. The golf cart batteries are true deep cycle and will last much longer. The 8D gives you double the capacity for a few dollars more and will last just as long, so why not get it instead? For some people its size and weight are overwhelming so the golf cart batteries are worth it. Also, if one cell of the golf cart battery goes bad, you can just replace that one battery instead of having to buy a whole new 8D. A company named Trojan makes some of the very best golf cart and deep cycle batteries. Their T105 costs about $130 each. A pair will cost $260 and give you 225 Ah of storage. They are better batteries and will last longer.
  • Flooded wet cell or AGM? So far we have only talked about traditional flooded wet cell batteries. There are two newer types of batteries:  gel and AGM (Absorbent Glass Matt). They have the advantage that they are sealed so that they don’t vent water or hydrogen, meaning they are zero maintenance and zero risk. You can also store them on their side, or even upside-down, making it easier to find a place for them. AGM batteries have all the advantages of gel, and none of gel’s disadvantages. An AGM charges faster, and discharges slower than a gel battery, nor are they as fragile, so unless you can get a gel really cheap, buy AGM. Again, they will cost double or triple the cost of a flooded cell battery, but their advantages may be worth it to you.
  • Where Will I Carry It? If you are living in a car, then you don’t have much room for a battery bank. Whatever you drive, you must also be aware of weight since the more weight you carry, the harder your engine works, and the less mpg you get. If you have a gel or AGM battery, you can put it anywhere it will fit, even on its side since it can’t leak. Maybe you can fit it on its side underneath the driver’s seat, or if you are alone, you can put them on the floorboards in front of the passenger seat. It’s a different story with regular flooded wet cells. They must be maintained regularly by keeping them full of water and cleaned off. They also vent hydrogen gas which is very corrosive, toxic, and explosive. Ideally they will not be in your living area. So where can you put 60-120 lbs. of battery? To be honest with you, I lived in a box van for 6 years with an 8D under my bed without any problem. Was it dangerous? Everyone tells me it was, but I never had any problem. I can’t recommend you do it, I can only report my experience. You can always buy or build a battery box and vent it to the outside if you are concerned about them venting. For my current camper, I bought something called Hydrocaps. They replace the battery cap that came on my battery and virtually eliminate water and hydrogen from escaping. Then I went to WalMart and found a plastic storage box that will hold my battery and keep it in there. That should contain the little hydrogen that does escape. So now I just keep it in the camper with me.

How will we Charge Our Batteries? Now we know which battery we will buy and where we will put it. Here are four ways to keep it charged.

1) Car alternator: We have a built in source of electricity in our car’s alternator, so let’s tap into it. This is fairly simple:

  • You need a cable long enough to go from your cars battery to your house battery. To measure this, tie one end of a string to the positive post of your car battery and wind it down, along the frame, and up to where the battery will be. Measure the string and this is how long your cable needs to be. Your town or a town nearby probably has a battery store or auto electric shop that will custom make a cable for you. Tell them the length you need and the size. With cables, the smaller the number, the bigger the physical size of the cable. A size 4 cable should be big enough for simply charging the battery but a 2 gauge is better because you won’t outgrow it in the future. Ask your retailer. They will also put the ends on for you. You will probably need to drill at least a half inch hole through the floor to get the cable in. Be sure and put a rubber grommet in the hole so the sharp metal doesn’t wear the rubber off the cable causing a short.
  • Your house battery needs to be grounded. Grounds are very important, so take your time and do it right. The best way is to run a 4 gauge wire from the negative of your house battery, through the hole you just drilled and to the frame of the vehicle. Look around and find a hole in the frame. I was lucky and found a hole close by. If you can’t find a hole, look for a bolt to take off and use it for a ground. If you can’t find anything, drill a new hole. Scrub the area around the connection with a tool until you have shiny new metal. I used an old knife. Then I put on a thin layer of Vaseline to keep rust from forming. You may be tempted to go directly to the body because it’s so easy, but there isn’t enough metal mass to be an adequate ground. That’s because bodies are attached to the frame with a rubber gasket to give a better ride.
  • Next, attach the cable ends to the positive pole of the house and starting battery and you are in business! Your house battery is being charged by your car alternator.


However, we still have a problem. If we use too much juice in our house battery, it pulls whatever is needed from the starter battery. If it draws too much, it won’t start the car and we are stranded. Do that a few times and we are buying a new starting battery. There are three solutions to this problem.

  • The first and simplest is a battery selector switch. You attach the cable from the starting battery to this switch and run a cable from the switch to the house battery. When you are going to be using the house battery, you turn the switch to off. This isolates the house battery from the starting battery so it can’t draw it down. The next day, when you are done camping and about to drive off, turn the switch to on and now the two batteries are connected again and the house battery is being recharged. Simple and easy. But what if you forget to turn the switch off? You run the risk of running your starting battery down and being stranded. One way around this is replace your starting battery with a marine starting battery which will not be damaged if you forget to turn the switch off. And carry a jumper battery as discussed earlier.
  • The next solution is a little more complex but solves all of our problems. It is using a continuous duty solenoid between the two batteries. A good auto store will sell these or you can Google “continuous duty solenoid” and order one over the net. Don’t buy an intermittent duty solenoid, it won’t last. It must say continuous duty. Once you have it, you mount it to the firewall of your vehicle. A cable runs from the starting battery positive post to one of the large studs on the solenoid. A cable leaves the other large post and runs back to the positive post of your house battery. On some solenoids there will be two smaller posts. One is for a ground to the frame, the other is to a hot wire in the vehicle wiring harness. Some solenoids are self-grounding, so they only have one of the small posts. The screws that secure it to the firewall act as the ground. If that is what you have, take extra care to have a good clean connection for the ground. If there is paint on the fender or firewall where you are attaching the solenoid, you must scrap the paint off so that you have a clean metal-to-metal connection. That thin layer of paint will prevent a good ground. Whether you have one or two smaller posts, you must run a wire to the vehicle wiring harness. Wherever you splice in, it must be after the ignition, so that when you turn the key off, power is turned off to the solenoid as well. A good easy place for this is the power to the radio since we know that when you turn off the key, the radio loses power and turns off. What happens is that when you turn on the key, power goes to the solenoid which activates a magnet inside it. The magnet lifts a bar which makes a connection between the two large posts, allowing charging current to flow from the starting battery to the house battery. When you turn the key off, current no longer flows to the solenoid, the magnet turns off, the bar falls and there is no longer a connection between house and starting battery. That means that if the engine is running, the house battery is being charged, and if it is off, the house battery cannot run down the starting battery. The best of both worlds! Absolutely no drawbacks.
  • Another solution, and by far the most common, is using a battery isolator. These are commonly available at any auto parts or RV store. Because these have a half volt drop between the house and starting battery, I don’t recommend them. Therefore, I am not going to cover them very much. Just follow the instructions that come with them if you want to use one.

2) Charging from a generator: For several reasons I won’t go into, just charging off the alternator won’t be adequate to keep your battery fully charged. A great answer is a generator. You may think a generator isn’t for you because of their many problems: there isn’t room in your car/van/RV, they are too heavy to lift in and out, they are too hard to start. When they are running, they are so loud they drive you crazy, plus they burn too much gas. All of that is true of past models of generators, but fortunately none of it is true of a new generation of Honda and Yamaha generators. They are tiny, light, quiet, start easily and sip gas. And they will run very close to forever. You may think I am exaggerating but seeing is believing. Visit a Honda or Yamaha dealer and be amazed how practical they are for car/van/RV living. The one problem is that they are fairly expensive. You can get the 1000 watt model for about $700 over the net. If you have the money, they are worth it. A 2000 model is about $950 but it has enough power to run a microwave, portable electric heater, or small portable or window air conditioner. For many people they are the ideal solution.

3) Park in an RV park. Once a week you can stay in an RV park to charge your batteries. While you are there you can do your laundry, wash your dishes and take a hot shower. Many offer cable TV and Internet access as well. If you pay $20 a night, that is $1040 per year. You could have paid for a generator and had money left over for that. Of course $20 a week is much easier to come up with than $700 cash so maybe it is worth it to you. Whether you are charging your battery at an RV park or with a generator, you will need a battery charger. Your first thought is that any old automotive battery charger will do, but that isn’t correct. Deep cycle batteries are fussy on how they like to be charged. A regular charger will lead to poorly charged batteries and their premature death. What we need is a “smart” charger. Very often they literally will say “smart” on the package. These are three stage chargers that automatically go through bulk, absorption, and trickle phases. They will charge your battery faster and make them last much longer.

4) Install solar panels. This is the ideal solution but it has several drawbacks. First it is expensive. A single 135 watt panel with controller and wiring will be at least $500-$600. Second, on cloudy or rainy days, during winter, or if you are parked in trees, they deliver less power, maybe not enough to meet your needs. Third, you may not have room for them on your roof. If you have the room and money and live in an area with good sun they are the best possible way to go. I love mine and wouldn’t be without it. Having all the power I need, for free, for the rest of my life is just an astounding thing! But I also have a Honda 1000 generator for times when I run out of power. Look for more details on the pages covering solar power basics elsewhere on this site. 

This has been a brief overview of RV electrical systems. I have tried to keep it simple enough to not overwhelm you, but informative enough to help you. A Google search of any of these topics will bring you a wealth of information. A good book which covers all this is:  “Managing 12 Volts: How To Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems”  – by Harold Barre


This is an important formula for you to know. Whenever you buy any electrical appliance it will come with a plate on it somewhere that tells you either its volts or amps. Using this formula you can know how much power it is going to draw off your batteries.

Amps X

Volts =





Watts /

Volts =





The formula is Amps times Volts equals Watts. So, if the plate on the item says it’s 10 amps, and it is a 12 volt item, then you can use the formula to know it is 120 watts. If the plate tells you the watts but not the amps, we can use this formula to figure out the amps. Watts divided by Volts equals Amps

Why is it important to know this formula? Your deep cycle battery’s storage capacity is measured in amp hours. For example it may be 100 amp hours. You don’t ever want to use more than half the battery’s capacity without recharging, so you have 50 amps available. So, if you use the formula to determine your fan uses 5 amps an hour, you know you can only use the fan 10 hours a day before you have used all the power you safely can.

Finally, it’s important to remember that even if the item is 110 volt, but you are running it off your inverter connected to the batteries, you divide the watts by 12 instead of 110.



1 Comment

  1. Dennis Crowley

    Hi Bob,

    I know how busy you are so I am hoping that I am catching you at a good time. Then again, it isn’t a “good time” right now for any of us.

    I spent the winter in my van north of Needles in the Arizona desert and used libraries, etc. to charge things up when I needed. And then the pandemic hit. Thankfully, I have friends south of Phoenix so I have been hanging out with them for the moment. And, needless to say, this time has been spent going over solutions for me to get electricity into my van which I now know is a necessity. And now because of the stimulus check, I have the means to do something as I live on Social Security Retirement.

    Trust me when I tell you that I have done a LOT of research into all the options and then all the options within the options. Ideally, I would have a solar setup as well as a charging setup for the house battery via using the alternator. And neither is cheap as you know. However, in order to get the ball rolling on this I had an idea that I was wondering if you thought that it would work.

    What I was wondering was is if I could use a battery charger to top off the AGM house battery by plugging it into an inverter such as one by Cobra which would then be plugging into my van’s cigarette lighter? It seemed to me that this would by pass all the expense of setting up a dual battery system that would reguire using a DC to DC charger because of the different charging needs for the AGM batteries. I do drive every day typically so this would allow the AGM battery to get some charge. Then once still, I could do a small solar panel setup to keep the battery topped off.

    I did read on your electricity post that you also use a generator which I guess would also be an option depending on how far I could stretch the funds. I was actually referred to doing this today by an RV mechanic in Tucson who recommended the inverter generator that Harbor Freight sells, the Predator 2000 which is about half the cost of a Honda.

    I am living in a 2001 Chevy Astro van so space has definitely played into all this. When I did the buildout on the van last summer I intentionally left space at the back passenger side so that I could place a house battery. This space would also work for a small inverter generator. Still, I am concerned about the fumes, etc. from the gasoline both from the generator and the gas can. Am I correct?

    Anyway, I know that you are busy and I hope that you will have the time to read and respond. I hope that this finds you will in the midst of things.

    Dennis Crowley

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