Chapter 4: Introduction to RV Electricity 12 Volts Direct Current (DC)

Required statement:  Links in this chapter are to tools I have purchased via Amazon and I am an Amazon affiliate so I will make a small commission off of everything you purchase via my links, there is no extra cost to you.

Links to items are here:


There are different types of batteries, the most common is probably known as the “flooded cell” battery, these are batteries with acid in them and require maintenance, you must keep the water level in those batteries maintained to the top of the cells.  They have removable caps, and you can fill them up with distilled water.  Check out Chapter 9 in the book for the link to the video on how to do it safely.

Colored Wire

You will find black, red, white, copper, green and possibly purple, blue, yellow, green, various striped and banded colored wires all over your RV.  I can’t stress the next statement: Use your phone or a camera to take pictures of everything BEFORE you start disconnecting wires from anything in your RV especially your battery”, this becomes very important if you have batteries hooked up in series, parallel both if you have 6V batteries in your RV.


Now most fuses in this converter are 15 amp for the DC power.  You normally want to carry a couple of each type of fuse as replacements.

Wait, what are those two 40-amp fuses?  They are reverse polarity fuses.  Huh?  So, let us take an example, true story for a client of mine.  Someone asked me about why their battery is not being charged but the 12-volt devices are working while plugged into shore power, but battery is dying.  I take off the battery box lid as I want to check the voltage on the battery, I open it and I see black wire on the negative pole on the battery and white wire on the positive side of the battery.  The wires got hooked up backwards on the battery since it is easy to confuse when hooking up to a battery black/white versus red/black.

Those two 40-amp (some RVs have 30-amp instead) fuses are reverse-polarity fuses to protect in case the wires to the battery get hooked up backwards, protection for your converter.

Keep a couple of those fuses also in your toolbox just in case you make the mistake of hooking up the wires backwards.

I disconnected the shore power, turned the battery disconnect switch so no amps will be pulled from the battery, pulled off the wires, replaced the 40-amp fuses, put the black wire back on positive pole, white on negative pole on the battery (always remove negative wire first and put it on last), turned battery disconnect back off (so battery power is flowing) and then the converter began charging the battery, all is good.  Here is link to a good assortment of fuses, just make sure you are getting the correct kind, in my RV, they are the normal sized fuses.

Positive and Negative Poles

Make sure to look at the + and – when disconnecting and connecting wires from your batteries, even better tape the wires (especially if you have multi-colored wires) with black electrical tape for negative pole and red electrical tape for positive pole wires.

Safety when working with batteries

You must keep in mind that when you are hooking up wires to a battery, there are 2 wires, if it is black/white wires (and this is usually on a label on the RV somewhere, like tongue area, on a travel trailer, where battery is telling you that black goes to positive and white goes to negative pole on the battery), if they wires are red/black, normally red goes to positive and black goes to negative but as stated above, taking a picture of your setup right now so you have it for the future.

Let us talk about disconnecting and connecting batteries wires.  First thing you want to do is look to see if your RV has a battery disconnect switch and move it to the “off” position meaning disconnect your RV from the battery.

As you look at the battery, look at which pole of the battery is the negative one, that is the cable you want to remove first.  After you have removed the negative cable, MOVE IT OUT OF THE WAY so it cannot accidentally touch the negative pole of the battery again while you are touching/disconnecting the positive side of the battery.  You do not want sparks or to get shocked by batteries.