Alan Tolle wrote:

 To Finn Lassen:

If you use a sealed gel cell type battery (weight of 23 pounds) it should be
installed just forward of the wing main spar in the cockpit, centered
between the two supports for the engine mount  5th and 6th attach points.

I had to make some presumptions here regarding the weight and balance data
Van now furnishes in the RV-3 builder's manual.  From the aircraft empty
weight listed the engine installed should be a Lycoming 0320 with full
electrical system and a wood prop.  The example lists a fuselage fuel tank,
so the battery should be at the rear of the baggage compartment.   The
baggage load was kept at 30 pounds.  For low fuel aft CG considerations, the
wing tanks should be used last.

With 55 gallons of gas you are going to have to carry a coffee can --- maybe
two coffee cans.

Just a thought.  I am a little concerned about the lack of redundancy in a
voltage dependent installation with only one battery.   In the 45 years I
have been putsying around in the air most of the mechanical failures I have
experienced have been electrical.  Yes, two were battery failures in flight
and would have ended in disaster had the engine depended on 12 volts.

I used two sealed motorcycle batteries of 14  amp-hour rating each in the
RV-3.   The system was wired to run on either one or both.  I always flew
the aircraft on both, and both were continuously charged.  One battery would
sustain the ignition system and fuel pump for at least  an hour and a half.
One battery would also start the engine but in practice I always used both.

The dual battery installation is a little more of work and weight, but IMHO
the safety of redundancy is worth it.   It is worth some consideration.

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