1. Simplest solution is a dumb charger that doesn't know whether it is
attached to a battery or not... That will put out DC power, no matter
what, which will provide the Piper solenoid with current to operate...
Of course, a dumb charger will over charge to 15 or 16 volts and boil
off the electrolyte over time...
Now, the solution here is to reduce the primary voltage to the charger
so that the charging voltage does not exceed 13.4 volts DC in trickle
mode... This can be as simple as a light bulb socket from the hardware
store wired to a duplex plug in SERIES, so that the 110 volt current
goes through the bulb and then through the 110v cord to the charger...
By selecting a small enough wattage bulb you will limit the voltage and
current to the charger which will hold down the battery voltage to 13.4
v under trickle conditions... You can play with the bulb size at home
using your car as the airplane battery until you get the correct
wattage bulb..
2. Next solution is to have a small battery attached to the output of
the charger which will supply the load to activate the charger and also
to operate the solenoid in the plane..

3.. Best solution! Have your mechanic change the Positive lead from
the Piper plug so that it goes around the solenoid and directly to the
battery... This is how I have Fat Albert The Apache wired (and every
airplane I have ever owned) for charging and jump starting...

denny