Blaaaaaaaaaaah!  We woke up to the shriek of the propane detector at 5 am in a parking lot outside a completely full campground on Natchez Trace.  We had arrived exhausted after changing a flat tire – in the rain – very late the night before and found no available campsites.  It was an unpleasant way of learning that the propane detector in our new-to-us Roadtrek is also an excellent low battery alarm.  We knew our single house battery of unknown vintage might be weak. But until we spent a night unplugged and needing the furnace, we hadn’t experienced a problem.

If you spend all your time in campgrounds plugged into shore power, you needn’t concern yourself much with the house battery or batteries.  Just remember not to leave your 3-way fridge running on battery when you spend 3 hours in a museum (switch to propane).  But if you spend much time boondocking (unplugged) you should know how much power you’re using and how much you have left.  One internet site on adding solar to your RV said the first step should be to install a battery monitor and learn how much power you use.  Only then you can design a good solar system for your needs.

Trimetric showing battery at 100%

Trimetric 2025RV shows the battery at 100%

We replaced our old battery and we also bought a battery monitor – a Trimetric 2025RV – from We agree that it has been one of the most useful upgrades we have made to our Roadtrek.  The box arrived with a wiring harness long enough for a Prevost, a rather intimidating 500 amp shunt, and the display to be mounted on the wall.  We looked at it and scratched our heads.  Maybe the local RV dealer would install it?  They were less than enthusiastic, so we carefully read the instructions and did it ourselves.  It was actually quite easy.

Installing the shunt requires mounting it in a  location near the battery. Buy a short piece of heavy battery cable, available at auto parts stores, to run from the negative terminal on the battery to the shunt, with the original negative cable attached to the other terminal on the shunt.   We ran the wiring harness for the monitor behind the wall panel into the pantry cabinet.  We mounted the display on the pantry wall above the TV.

Shunt Installed

Shunt on left outside of battery compartment, holes into compartment not yet sealed

With the Trimetric battery monitor installed, we quickly learned and made notes of how much power each item in our Roadtrek used.  In addition to the voltage of up to 2 batteries, the Trimetric can display the number of amps being used –or watts if you prefer  Don’t deplete a wet cell battery below 50%. The Trimetric has a nice display of % full.  Our single deep cycle battery is 80 amp hours.  Those with two 6 volt batteries may have as much as 220 amp hours.  So we had 40 amp hours to use before recharging, either by driving, plugging into shore power,  running generator, or by solar.    Here is what we discovered:  Your Roadtrek may be different, so make your own chart.

Power Use ChartFor example, using the table, if we run the Fantastic Fan on 2 overnight – say 10 hours – it will use 1.5 amps times 10 hours or 15 amp hours.  If we watch a DVD for 2 hours, that would use 1.5 amps x 2 hours or 3 amp hours.  Meanwhile the sensors work all the time, plus the Snyder kit on our fridge runs, so we have a constant draw of 0.4 amp hours. If we are stationary (and unplugged) for 12 hours that would add 0.4 x 12 for 4.8 amp hours.  So we will be using 15 + 3 + 4.8 = 22.8 amp hours — well within our 40 amp hours available.  Our biggest power hog is our laptop computers.  We use 12 volt adapters, but they can still use 3-5 amps.  We are careful with our computer use when boondocking.  We learned that we rarely exceeded 30 amp hours a day in power – which is probably on the low side for most Roadtrekers.

With a battery monitor you can keep an eye on your power use and prevent damage to your battery or batteries by not allowing them to discharge too far.  It will give you peace of mind when you wonder if you have enough power to run a CPAP machine or a furnace through the night.  It’ll provide you with the information you need about your power needs when you consider upgrades to your batteries or charging system,  or adding a solar system.

Trimetric Diagram