Piper Archer - Headphones drains the battery ?

When we bought our Piper Archer 2 years ago the previous owner cautioned
about leaving headphones plugged in in the rear seats.
He reckoned that with the headphones plugged in the battery would be slowly
drained.
I dismissed this caution as it did not seem to make any sense from an
electrical point of view.

When I came to start the engine yesterday, the cranking was very slow and
seemed like the battery was right down.
We have a new battery fitted a few months ago, so I doubt that as the
problem.
After flying for a couple of hours the engine cranking was back to its
normal speed.

I took a good look at the alternator and belt and nothing obvious was
noticed.
However, I noticed that a pair of unused headphones was plugged into a set
of the rear seat jack sockets.
They had been plugged in for about 2 weeks.

Now I wonder if they caused a slow drain on the battery while the bird sat
in the hanger for a couple of weeks ?

The aircraft has a SP400 intercom and an avionics master switch which is
always switched off when the engine is shut down.
The avionic line up is:-
KMA20, 2 x KX170's, KT76, KR86 and Flybuddy 820.

Maybe the old owner was correct ?
But what would cause the phones to take current off the battery ?

What does this knowledge base think ?


--
Roy
N5804F Piper Archer

"I have had some bad landings but I have never missed the runway"