Battery being drained
Something is draining my 2008 Toyota
Highlander, if I don't drive it for a couple of
days it won't start and I need to boost it.
Diagnosing A Car Battery That Runs Down: http://www.aa1car.com/library/battery_runs_down.htm - How to Find a Parasitic Battery Drain: http://www.wikihow.com/Find-a-Parasitic-Battery-Drain - you should also get the charging system (battery, alternator) tested, you can get that done for free at any of the major auto parts stores.
charge it up, disconnect the ground and let it sit, if it starts a few days later you are correct somethings pulling it down while connected and not the battery plates shorted and internally draining it., darn near half of condemned batteries traded in are still good, like pcm,s used to be,
I've done that and have replaced it with a new battery and still the same issue. Tried every relay and fuse as well. Been trying it all.
turns out it was the celenoid for the starter.
I wondered about that. My 2005 Highlander dies after several days in the garage, but only in Winter. The dealership says I just don't drive enough, and says the solenoid is unlikely to be the problem (but they will happily charge me $450 to replace them). I've had previous cars that could sit outside for weeks and start right up, so I never trusted the "not driving enough" claim. And I'm going to try that "disconnecting the battery ground" test. Together, we may pin down the Toyota battery problem...
Good luck. It was a long process to figure that out.
My sister has a 2017 Highlander XLE. Same problem. Same time frame (two or three days idle). They have put 3 new batteries in the vehicle. They want her to run a trickle charger. What a bunch of bull. The last "expert" wondered if her home wifi connection was too close to the garage. WTF! They say the solenoid isn't the problem.
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