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Highlander Hybrid 12 Volt Battery

I and a number of other Highlander Hybrid (HH) owners are having a problem with the 12 volt battery discharging. Most of us are experiencing the problem at intermittent intervals. Toyota maintains there is no problem since it cannot be replicated at the Dealer Service Department. We are not leaving lights on, doors ajar or doing anything that should cause this. The problem is across all three years the car has been produced - 2006, 2007, and 2008.

Can anyone help with the issue?

We’ve heard a few people complaining about this on the board. I’m not sure why it seems to be more prevalent with the Highlander, but it seems that with most of the hybrids if you leave them to sit for much more than a week or so the batteries usually discharge. It’s a combination of the fact that the little 12v battery has a much lower capacity than a regular car battery and that there’s so many little electronic gizmos in hybrids that need power at all times. I wonder if, since it’s more of a luxury car, there’s a feature the Highlander has that the Prius, etc doesn’t that drains the battery.

It doesn’t even have to be a week or so. Mine has discharged in 2 days. On a Toyota forum there was one that did it within 3 hours. No rhyme or reason, all sorts of weather, car left in garage or outside, nothing seems to give you an AHHA moment - that must be it.

Perhaps poorly designed/manufactured batteries.

Have they been revised or improved upon in any form? (I guess not eh?)

Are the batteries all from the same manufacturer?

Not grounded properly?

I doubt I’ll ever be driving a hybrid like these, way too many bugs.

Hmm… I wonder if it’s possible to check one of these batteries using a conventional battery tester. It does sound like a bad battery.

I’ve had mine towed to the dealer twice, the first time they said the battery had no charge at all, the second it read 5 volts - not enough to start it. It’s the 12 volt in the engine compartment, so can be tested with a regular battery tester.

I think they are two small, it is a very small place.
Batteries run the gamut from factory installed to user replaced to replaced by a Toyota Service department. Doesn’t seem to make a difference.

It would be nice to know what the charging limits of the alternator are along with the load requirments of the electrical system. The battery may not be getting the proper charging current it needs to maintain a good charge. I assume the trouble isn’t due to some drain on the battery while the vehicle is parked.

Every problem we have experienced has come after we left the fob in the car. I agree the car is pretty unforgiving about leaving a door or a hatch or even the rear pop-up window open. This is true even if there are no lights visible.

That vehicle uses a special type of battery called an AGM. Partly may be due to the fact that the battery is located in the passenger compartment, AGM’s are safer for that application than the traditional flooded battery. The downside is that AGM’s are finicky about the rate they are charged. If too fast, the charging can damage them. So be sure to consult a dealership about the proper way and which equipment is best to charge your battery if it ever needs to be manually charged.

If testing shows your battery remains in good condition but the car is draining it overnight for some reason, that’s diagnosed by monitoring the drain current. It should be in the 20-50 mA range when everything is turned off. If your shop can catch it above that range then they should be able to figure out what circuit is causing the problem by thermally monitoring the various fuses with a thermal imager. The fuse that is getting hot is the circuit that’s causing the drain. Has that been done?

Common causes of phantom battery drains reported here

  • Door ajar
  • Wind blows on door, affects door switch, which keeps computers turned on
  • Hood/trunk/glove compartment light etc remaining on
  • Alarm system
  • Entertainment systems, especially non-original equipment versions.