How often do you drive the vehicle? If not offend then a trickle charger on the 12V battery will help.
If you drive it at least a few times a week you probably have a parasitic draw on the battery, which will need to be looked at by a mechanic.

 

I probably do not drive it enough. A 12v battery should be OK for two weeks , if it was fully charged. I don't not think Toyota is fully charging the 12v battery. Or maybe they just use really bad 12v batteries?

Is there a secret way to let my big battery charge my little battery?

 

I probably do not drive it enough. A 12v battery should be OK for two weeks , if it was fully charged. I don't not think Toyota is fully charging the 12v battery. Or maybe they just use really bad 12v batteries?

I would take it to Autozone or a similar and have them test the battery. It might have a bad cell.

Is there a secret way to let my big battery charge my little battery?

No

 

I would take it to Autozone or a similar and have them test the battery. It might have a bad cell.

No

Bummer. The hybrid battery is pretty big. It is too bad I can't use it to jump start the car!

 

Just had the same problem with my wife's hybrid Lexus. Had to take it to local Toyota dealer to have the check engine light turned off after getting the car started. I was told by them that if I'm not going to use the vehicle for a prolonged period of time to put it on a trickle charger. Also to keep or store the key fob 30 feet away from the vehicle as it states in the owners manual. Apparently if the key fob is any closer all the electronics in the hybrid vehicle do not shut down and you have a constant drain on that small starting battery. If thats impossible look into buying a "Faraday bag" sold by Amazon or Walmart to prevent the key fob from sending signals to the car when parked eliminating the drain on the battery.

 

Just had the same problem with my wife's hybrid Lexus. Had to take it to local Toyota dealer to have the check engine light turned off after getting the car started. I was told by them that if I'm not going to use the vehicle for a prolonged period of time to put it on a trickle charger. Also to keep or store the key fob 30 feet away from the vehicle as it states in the owners manual. Apparently if the key fob is any closer all the electronics in the hybrid vehicle do not shut down and you have a constant drain on that small starting battery. If that's impossible look into buying a "Faraday bag" sold by Amazon or Walmart to prevent the key fob from sending signals to the car when parked eliminating the drain on the battery.

There is another reason to keep the fob far away - relay attack that allows thieves to steal your car quickly and quietly. They use an antenna and scan the garage or street facing room for the FOB's signal, then replay this signal to the car while being next to it. This way they can open and start the car as if the fob was next to the car itself. You can buy a box or pouch that block the signal or just keep the fob far away from the car and the street

 

Keep your FOB's in a Faraday Bag. Inexpensive extra protection from both battery drain and auto theft.

 

A cheap piece of aluminum foil folded in to pocket will do exactly the same.

 

FWIW: Pressing and holding the lock button on the fob and hitting the unlock button twice will turn off the fob. The little red light will flash 4 times. When you take it near the car, you won't able to open the locked doors or hatch by touch until you hit a button on the fob to wake it up.

 

This makes alotta sense. Just had my 2023 HH battery replaced it had 2 dead cells. I hadn't driven it in a week & batt discharged (manual says it's normal) Toyota upgraded batt from a 345cca to a 540cca. Parasitic drains are frustrating to diagnose, I gave up on my 2004 Honda Odyssey due to a pd. 2 days ago, our Highlander got stuck in a costco parking lot as the battery went kaput.

 

The 12V battery should last longer. We have left my wife's NX 350h for a couple of months parked in the garage without problem. Do you have any aftermarket accessories?

 

I purchased one of those Li-Ion battery jump start units before X-mas when Amazon had them on sale and threw it in the back. I haven't used it yet but since my HiHy is over 3 years old now and in a hot climate I know the battery could die anytime unexpectedly. Hoping it will at least get me going to drive to buy a new battery if/when the time comes. I hate being stranded and having to wait for assistance to come and jump start a car.

 

You probably have a parasitic draw. Find a YT video from AMD explaining it and how to find it.