There is always drain on the battery even when the interior lights are shut off with the master switch. A variety of components draw power when the ignition is off which is why it's not necessary to reprogram some features except when the battery is disconnected. The keyless entry is always in "receive mode". And the fuel evap system goes into some sort of self checking procedure on a routine basis - if you hear a buzzing from the back of the Sienna late at night when the ignition is off, that's what it is unless it's a bunch of mice having a party. On some Sienna trims it's impossible to turn off all the interior lights when the doors are open, e.g. the front door courtesy lights on my Sienna Limited come on when the doors are open even when interior light master switch is set to off.

For all I know, my Sienna could be in constant communication with the mother ship. Maybe it is since my Safety Connect agreement mentions that it is "periodically transmitting your Vehicle’s Vehicle Health Information and Multimedia Screen Operation Log Information to Toyota".

I doubt that you have anything to worry about. All the interior lights in my Sienna have been left on overnight on several occasions and there was no noticeable harmful effect.

 

I appreciate the comment. When camping I have been known to leave the doors and hatches open all day.

 

Not sure what model year you have there. But the sienna has a feature that turns off the interior lights automatically after 30-45 min of use when either one or all the doors are left opened.

 

That's a good point. Seems if I just turn off the master switch that will take care of any interior lighting current draw.