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Of all the questions I’ve been asked about RVing, this one is probably the most frequent.  Ever since we installed large lithium batteries from Lithionics in Lance 5 years ago, that seems to be mostly what people want to know.

Unfortunately, there’s been no way to answer that question without a million qualifiers.  Until now.  In this video, I give you a little sneek peek at our 20k upgrade, and introduce something I’m calling a

Normalized Runtime Estimate.


The whole idea behind the NRE (Normalized Runtime Estimate) is to create a metric that does two things:

  1. Allows us, the RVing public, to compare one rig to another using facts – instead of guesses and anecdotes.
  2. Create a “worst case” runtime estimate for any of these systems.  Something that most people should be able to beat in actual use.  It’s your safety number.

I think I’ve done that, and it only requires three pieces of information to get there:

  • The first input is the USABLE battery capacity, expressed in WATT-HOURS. (Bu)
  • The second input is the inverter efficiency (E)
  • And the third is the running watts of the air conditioner in question (L)


That’s it!  One multiplication, one division, and we have a standard way to describe these systems.

You can watch the video to get the complete description of how and why, and all the reasoning behind things, but that’s the formula.


we can start using NRE instead of relying on oftentimes not very relevant experiments or isolated reports that may or may not have anything to do with your particular situation.  The NRE formula eliminates the ‘yeah but’ variables, and brings things down to just plain data.

The next time you’re talking to an RV sales person, or to a manufacturer’s rep… ask them for the NRE of their battery/inverter/air conditioner system.  If we all start asking for it, they’ll have to start providing it.

Remember – someone had to be the first person to ask for “miles per gallon”… and the NRE formula has far less variability than that!

Let’s hear it down in the comments.  What do you think?