Common understanding is that the car goes into a "deep sleep" after sitting a while (a week, a month?) to save the battery. Remotes will not work anymore. You can wake it by opening the car door with the key (might work with the trunk too). In theory, this saves the battery. Are you sure yours is dead?

 

Depending upon the age and condition of the battery, that could indeed be a long time to sit. Charge it up and see if it comes back to life....

 

My car is the same, maximum 3-4 weeks without being used to be able to open door or trunk with remote. So when I leave it in the garage for long periods I always charge the battery every now and then or disonnects the battery

Regards,
Higgins

 

 

 

In addition to the above comments, make sure that the little door/flap on the ignition switch closes properly when the key is removed. If not, then the car still believes that the key is inserted and a lot of the electronics keep running 24/7.

 

my experience is locking the car while on tender charges it more quickly and completely, no current being used when locked compared to just sitting there unlocked

 

That's interesting.

 

^^^^^^^ this.

wet cell batteries will last much longer if a modern batter tender is always on the car when not being driven overnight or longer. A modern tender has the circuitry to keep the battery at 100% without overcharging it. Thanks to the battery tender + I've normally been getting 8 - 10 years from car batteries, sometimes longer.

Z

 

+1 Zray,

an experiment with two xk8's batteries yields the following, one an AGM the other Lead Acid, a 98 and 01. fully charged batteries tested after settling for 24 hrs to just over 12.6 volts, load test fine, less than one year old. both cars locked, note that the electronics do not differentiate between locked and unlocked state or state of the alarm, every door and lid closed does matter, although mine passively arms (factory unit, unmodified), no issues with either car, temps range between 55 and 35 F. 2.5 weeks later, both batteries test to 12.4 volts and load test fine. this is a magic number as allowing lower sulfates the cells. my previous life required equipment such as vehicles to be very well maintained and reliable due to the conditions, so have some experience here. this should guide people as to when to use a tender although constant is an absolute benefit. many engine heater connections actually integrate a battery maintainer for this very reason.

by design, see the owner's manuals, these vehicles do enter a lower power mode if locked for a longer period of time close to three weeks (forgot the exact time period) and the remote receiver is powered down along with a few other things. after this time a key must be used to unlock the car.

note that both test cars are factory correct with the cellular telephone hardware intact and powered, although unused. if a car discharges the battery more than the above and/or in a shorter period of time either battery or car has a problem.

a 15 minute drive with everything in working order will bring the battery to full voltage after a start when used on a somewhat regular basis.

easy test for the battery. turn key to run (dash lights test) and switch on the main beams, wait ten seconds, then start the car watching the voltmeter. it should not drop below 11 volts even at very low temperatures.