As my life has progressed, I've been:

• backpacking in the Sierra Nevada
• tent camping from the back of a motorcycle
• tent camping from the trunk of a passenger car
• tent camping from a van
• camping in a small travel trailer
• camping in a borrowed motor home (which I'll NEVER do again but that's another story)
• back to camping out of my travel trailer

Each time, it's become a little more complicated, mostly do to the electronic gadgets that I bring along. I didn't have a cell phone, iPod (and speakers) or laptop computer when I was tent camping, but now I can't seem to do without these toys. The problem is that ALL of these gadgets need electrical power of some kind and all have rechargeable batteries which always seem to be running down.

This tendency to bring along every modern electronic gadget is called "flash camping" in high tech new-speak.

All of these toys can recharge from a cigarette lighter or from a 110 VAC inverter plugged into a cigarette lighter. However, the power still has to come from somewhere and ultimately that somewhere is the alternator in my truck, usually via the truck battery. Dry camping in a trailer without a generator means that everything electrical in the trailer runs from the trailer domestic batteries. Those batteries need to be recharged after a few days as well, either from the truck while the trailer is being towed or from shore power when available.

The loads in the trailer itself are significant enough for the domestic batteries. Adding the recharge loads of all of these toys is just too much. I need those trailer batteries for domestic functions so another way is needed to recharge the toys. This page describes that other way that I use to keep the toys charged.

Batteries are rated in amp-hours. This is the product of the current available multiplied by time. A typical small RV battery is capable of supplying 40 amp-hours. This means that it can supply 1 amp for 40 hours, 10 amps for 4 hours or 40 amps for 1 hour. The more current that is drawn, the quicker the battery goes dead.

This is a table of the loads in my trailer. Other RVs should be similar.

Large RV loads, such as an electrically powered refrigerator or A/C typically run only from shore power. A refrigerator usually won't even work from a battery except to run the igniter when it is running from propane. However, SOME RV refrigerators CAN be set to run from +12 volts. These do draw significant power and can flatten a very large RV battery in a jiffy.

If the trailer batteries run down due to overuse, they must be recharged from the tow vehicle or the lights, pump and refrigerator igniter and other necessary goodies stop working. Recharging the trailer batteries from the regular trailer umbilical can take hours. This is ok if you are traveling anyway, but once you've reached your destination, your tow and trailer will seldom be connected. Even connecting the tow directly to the trailer battery with a set of jumper cables (to get a higher charge rate) means that the tow has to sit and idle for an hour or more to get another couple of days worth of juice into the domestic batteries.

I have two domestic batteries for the trailer. Normally, multiple batteries will be wired in parallel so that they charge and discharge together. However, I have installed cutoff switches on both of them so that I usually only keep one connected at a time. The switch on the nearest battery is in the open state. This way, I get a pretty solid indication when half of my capacity is consumed. I'll only close the switch to a battery that needs charging so that only that one gets charged. If you connect a charged and discharged battery together, one will inefficiently try to recharge the other.

The purple stuff all over the contacts is a spray on protective coating that helps prevent corrosion of the battery contacts. I got it at Pep Boys.

Recharging all my toys (especially computers) from the tow battery means that I run the risk of running down the tow battery so that it won't start. Recharging this stuff from the trailer domestic batteries can leave me without lights or water. This is bad.

What to do?

After several years of flattening batteries, I've iterated to a solution. I keep a THIRD full sized RV battery in the back of the tow. I've built an adaptor that allows me to recharge the extra battery from a cigarette lighter while driving anywhere. This battery then has the capacity to recharge a computer several times without running the risk of running down the tow vehicle battery. Further, if the tow does need a jump, it is easy to pull the extra battery out of the back of the tow and connect it to the regular battery with jumper cables (provided that it has not been flattened already by recharging computers).

Further, if I do run down both trailer domestic batteries, I can always swap one out (because I selected the same type of battery) and recharge the formally dead trailer battery while I am out sightseeing and the trailer is left in the campsite. With the modification described below, the extra battery can be plugged back into the cigarette lighter socket in the trailer to backfeed power to the trailer without removing the regular batteries. The regular batteries should be disconnected before this is done however, or the extra battery will try to charge the dead trailer batteries too.

If one camps in RV parks all the time, all this is unnecessary as there is access to shore power, but in National Park, National Forest, state or local campgrounds, shore power just isn't provided.

While camping, I usually drive somewhere to go sightseeing every day so that I have an opportunity to recharge the extra battery. The extra battery can be left plugged in most of the time. All I need to do is to remember to unplug it when I want to recharge something so that the tow vehicle battery doesn't supply part of the load too.

The basic setup is very simple. All that is needed is a 12 volt cigarette lighter extension cable and a pocket knife. The cable can be purchased at many RV stores for about $10.

To make the modification, simply strip about 1" of insulation from both wires somewhere near the middle of the cable. Then wrap the stripped wires around the screw battery posts of the spare RV battery. Unlike car batteries, RV batteries typically come with conventional round top posts and a screw on connection. Polarity IS VERY IMPORTANT. If it is wrong, a lot of smoke will appear very quickly. Either use a ohmmeter to trace out the wires or disassemble one end to trace the wires. The center contact of the plug or socket goes to the post marked +. If available, use a voltmeter to check to see that +12 is available on the center contacts of the plug an socket BEFORE anything gets plugged in. While the adaptor is not in use, plug them together to "safe" them and prevent a short circuit at the plug end.

The plug can then be inserted into a cigarette lighter socket to allow the battery to charge. A 12 volt load can be plugged into the socket end. Both ends can be used at the same time while driving. Then the battery just floats and the load will run from the tow vehicle's alternator. However, if the socket end is heavily loaded while being charged from the plug end, the net charge rate will be materially reduced due to the voltage drop in the wiring caused by the load. My truck has 3 jacks on the dash and one more in the back. I typically recharge the RV battery from the rear jack and connect the other equipment to be charged to the ones on the dash. This way, the load being charged doesn't drag down the charging voltage applied to the battery.

In the center of this photo is a conventional 150 watt inverter. This device converts the +12 volts from a car's electrical system to 110 VAC to run small loads like battery chargers. These devices are normally pretty efficient and waste little power to heat. On the left is a three way multiple power jack adaptor. This allows more than one 12 volt load to be plugged in at one time. This particular one has some handy little LEDs on it that indicate the voltage of battery. If your car or truck doesn't have multiple jacks, then this kind of gadget can come in handy.

For those of you that are electrically inclined, this little gadget is very handy. It is a clip on ammeter that can indicate pretty high currents, up to 60 amps. For diagnosing generator, or battery problems this guy is very useful. Just place the wire in question across the back of the meter and the meter will indicate the magnitude and direction of the current in the wire. It's not very sensitive or accurate, but it is sure better than guessing. I looked around for 30 years from the first time that I saw one of these before I found where to buy one. The are available from Hoyt in Penacook, N.H. The model number is 764.

This is another handy gadget. It is simply a DC voltmeter configured to plug in a cigarette lighter socket. It can be used in either the trailer or the tow to check system voltage. These can be found at RV supply stores.

With all my toys hooked up and charging I've got quite a load. I will be typically charging 3 laptops, 2 cell phones, AA batteries for my speakers, my iPod and my camcorder batteries, all at the same time while driving. By the time that I get to my next destination, all of these batteries are charged AND the spare RV battery is charged too, ready to recharge these goodies whenever needed.

The smaller USB stuff can charge from many USB sources, but there are some restrictions. Various methods of charging USB devices and various USB charging sources are described at my USB Charging Tips page.