Son has a 2004 Toyota Highlander Limited 200,000 miles ont it. Something keeps draining the battery after it sits for a day or so. Replaced alternator with a 130amp desno. Replaced the battery and same problem. Ther car is in great shape and regular maintenance. ?
first make sure something is not staying on. check map lights, glove box light, ect. check to see if brake lights are sticking on randomly, you can have a bad brake light switch sticking. make sure all your battery cables are clean and tight. both sides not just the battery side. after that then…
I own a much-loved first-gen Highlander. I agree with Weekend-warrior that a conventional battery-drain diagnosis is the best first step. However, I will say that mine had a period in its mid-life where it would drain itself oddly as well, to the point that it needed a jump. Often within a day or two. Shortly after that started, I needed a new alternator and battery. After they were replaced the weird battery drain stopped. Here in New England, I can go about 5 days before the Highlander has a tough time starting in dead of winter. It does not hold a charge as long as our other cars.
Many automotive fuses have contacts on the top that can be reached with fine tipped multimeter probes without removing the fuse. Set the meter to the 200mV range and then measure the Voltages across all the fuses to see what is drawing current. For instance, if a fuse as 0.01 ohms of resistance, a 1 Amp draw will show up as 10mV on the meter. Now you can find out what system is causing the draw. If you can find the door open switch and tape it closed or something you’ll be able to keep the door open while you work on it without triggering whatever draw happens when the door is open.
I think using a multimeter to measure parasitic current draw is the most effective way to get to the bottom of this
Another thing to consider . . .
Do NOT leave chargers plugged in
I have seen countless instances where even the tiny LED on the chargers draws enough current to kill a battery over time
And I’ll spell it out so that there can be no doubt whatsoever . . .
50 milliamps is the maximum allowable parasitic current draw, imo
Your SON’s Highlander… Maybe he has an aftermarket radio? Subs and amplifiers?? An android head unit? A dash cam? And as already mentioned, chargers for his phone.
All these can be problems as they age and draw a LOT more battery when off than they should. Check those first. Pull the fuse on each of those and see if the problem goes away.