Pretty much any charger will draw some current. Diodes have a very high resistance in the reverse direction, probably talking microamps here not milliamps, a dashboard clock will draw many times the current of this reverse-resistance load.

If you want to see if it is significant, and don't have a DC ammeter, try the smallest light bulb in series with the charger. Oh, another thing. If there is any kind of sensing circuit for reverse polarity hookups etc., such as a red light, it too could draw some current.

Typically when I store batteries long-term I use a small "ice-cube" type of 12v converter and a timer, have it hooked up and charging for an hour or less per day. The internal resistance of the battery isn't infinite either, it will self-discharge over time.

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Gone to the dark side

- Jeff