Welp, mighty good questions, ya got there, youngster.

The answers are, of course, "it depends."

Without knowing the design of the charger, a fellow can't easily know how
much current it parasites off the battery when unpowered. Now, one would
think, one would /hope/ that the designer said to hisself, "self, I'd best
make sure that my customers' batteries are not discharged if there is a
power outage at his or her house."

But one never knows, does one?

Use an ammeter.

A diode would take away 0.5 to 0.6V from the charge voltage, which is
pretty significant when considering how much voltage a battery needs in
order to be fully charged. 12.6V is full charge. 12.0V ain't.

--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR

On 11/13/2009 4:35 PM Jim Felder wrote:

> About a month ago, I mated a trickle charger with a cig lighter plug
> so I could plug up the westy electrical socket to a power source, plug
> the trickle charger in to the interior 110v socket, and plug the cig
> lighter plug into the receptacle on the bulkhead under the seat. No
> muss, no fuss, but not quite permanently wired in. That turned out to
> be a good thing, as I noticed on a recent camping trip that even with
> the charger unplugged from the interior 110 receptacle, the LED light
> on the charger glowed when the setup was plugged into the cig lighter
> socket. That means that the battery was feeding the charger.
>
> Is there any significant current loss going backward through the
> charger? Is it just running the LED, or is it running down my battery?
> I presume the proper diode in the proper place would stop this. Can
> anyone describe what I should to do modify?
>
> Jim
>