Digital Battery Voltage Monitor

Last time, I showed you some neat but pricey electronic gadgets. This time, I’ll go frugal with a simple electronic gadget that most every RVer needs: a digital battery voltage monitor.

Sure, a few top-of-the-line coaches come with good-quality, battery-voltage monitoring built in, but the average RVer is stuck with a few LEDs on the monitor panel. Surely, there needs to be more battery information available than just “Good – Fair – Low.” That’s where a digital panel meter shines! When used with the voltage chart, you can tell what’s up with your house batteries.

For you do-it-yourselfers, here’s a simple voltmeter that is inexpensive, easy and small enough to fit just about anywhere. The meter runs off a single 9-volt battery, and you can connect it to almost any wiring in the rig that carries unswitched 12V DC. The parts listed below are available from All Electronics Corp, 800-825-5432. Their Website is You can often find similar items at local electronics parts stores.

Parts list:
• 3 1/2 digit LCD digital voltmeter, panel mount, battery operated, 20V full scale. Part #PM-21 ($9)
• Small on-off toggle switch. Part #MTS-4 ($1)
• 9-volt transistor radio battery.
• 9-volt battery connector. Part #BST-3 ($1)

Follow the directions included with the panel meter. Attach the battery connector as specified in the meter instructions. Install the small toggle switch on the battery connector + lead. This is used to turn the meter on and off. You can omit this switch and have the meter on all the time, but it will run down the 9-volt battery in about six months. I chose to use the on/off switch on mine. Mount the meter in your rig in a convenient location, preferably near a 12-volt source. Closer to the battery is better but not critical. Connect the meter input to the 12-volt source. A fuse would be a good idea if the circuit that
you connect the meter to isn’t already fused. A 1A fuse will be more than enough as the meter draws little current.

Rather buy a meter ready-made for just a few dollars more?
Go to
This unit reads out voltage in hundredths of a volt and has adjustable alarm points and a lighted readout.
Thanks to Paul Nixon #103584 for finding this great gadget at a reasonable price.
For more battery system information, check out “The 12V
Side of Life” on my Website
Happy monitoring!

Complete Product Name: Digital Battery Voltage Monitor

Average Street Price: $15-$30

Original Publication Date: MA/10