For years I have flat towed my 2005 Odyssey behind my motor home, requiring that the ignition be in the aux position. To avoid draining the battery on longer trips, I attach a battery charger at the end of the day's travel. I have done this for years, but developed a problem in the past 6 months. Between 2 and 6 hours after attaching the charger the car alarm activates. Unlocking the car only temporarily stops the alarm. The status of the battery charge does not seem to matter. The alarm does not unexpectedly activate except when the charger is attached. Using a new charger did not remedy the problem. Any ideas about what is causing this problem or how I might resolve it?