Not sure what "too long" is to you, but I've had to jump or charge (depending on the urgency of a trip) our 245 camper/pickup truck when it has only been a week, and other times it starts up after three or four weeks.

The battery is 5 years old but that's new for our fleet. I suspect the usual frayed insulation on the driver's door central locking switch may be intermittently sucking the juice. Just haven't been able to catch it in the act yet.

When using it for a camper, I thought to check the parasites* before retiring for the night due to the inconvenience of getting a jump. The battery itself seems to be holding the charge, warm or cold.

Suggestion to self: Disconnect door switches from central locking. Easy to do right under an '89 245's dash, and non-issue given we have keyless entry on these cars.

*remove the negative terminal on the battery and measure current with everything turned off and the doors closed.
--
Art Benstein near Baltimore

Anybody who doesn't know what soap tastes like never washed a dog.
-Franklin P. Jones