Weird battery issue with Toyota CH-R

dirtychinchilla · 18 Mar 2025 at 09:03

Morning all,

My wife has a 2021 CH-R, which is a petrol hybrid. She didn’t drive it for four weeks after a C-section, and when I tried to start it, the 12V battery was flat. I put that down to it just not having been used. Obviously, I jump-started it, got it going, and for a few more weeks, it was fine.

Fast forward, and it’s now happened twice more, each time a few weeks to a month apart. She drives the car regularly - this week, she last drove it on Friday, and by Monday, it wouldn’t start again. Weirdly, on Monday morning, I moved it on the driveway, and it seemed fine, but a few hours later, when she and the baby tried to go out, it wouldn’t start.

These hybrids don’t have alternators, so that’s not the issue. The hybrid battery seems to be charged and the two most recent times there has been enough juice to get the lights on etc, so I’m a bit stumped. Anyone got any ideas? I was thinking of just replacing the battery and hoping for the best!

Thanks in advance,

dirtychinchilla

JonRGV250 · 18 Mar 2025 at 09:12

Fit a new aux battery (12v), or fully charge the old one and test, the same happened on my mothers 2022 Yaris hybrid.
Also, under no circumstance leave the car in neutral with radio, lights etc on, it’ll kill the 12v in minutes.
It doesn’t take much of a drop in the 12v for the car not to start.

dirtychinchilla · 18 Mar 2025 at 09:16

JonRGV250 said:
Fit a new aux battery (12v), or fully charge the old one and test, the same happened on my mothers 2022 Yaris hybrid.
Also, under no circumstance leave the car in neutral with radio, lights etc on, it’ll kill the 12v in minutes.
It doesn’t take much of a drop in the 12v for the car not to start.

Cheers. That's probably what'll happen.

I don't understand how it's not getting fully charged.

Yaayuh! · 18 Mar 2025 at 09:21

Might not be able to hold the charge properly anymore since the first major discharge might have damaged it.

Just replace it.

JonRGV250 · 18 Mar 2025 at 09:28

dirtychinchilla said:
Cheers. That's probably what'll happen.

I don't understand how it's not getting fully charged.

If you want to give it a good charge before replacing it then turn the car on a let it idle for 20 minutes (the engine will keep stopping and starting, but it’ll quickly charge the aux battery) then see how you get on.
But the 12v is 4 years old and it wouldn’t be a bad idea to replace it just for peace of mind.

dirtychinchilla · 18 Mar 2025 at 09:29

JonRGV250 said:
If you want to give it a good charge before replacing it then turn the car on a let it idle for 20 minutes (the engine will keep stopping and starting, but it’ll quickly charge the aux battery) then see how you get on.
But the 12v is 4 years old and it wouldn’t be a bad idea to replace it just for peace of mind.

I left it running for something like an hour the last time it happened. Thanks for the advice though. I think you and I are right! Just replace the battery and hope that solves it.

Fortunately the car is a lease through work so it'll get replaced by them.

Manbatius · 18 Mar 2025 at 13:18

dirtychinchilla said:
I left it running for something like an hour the last time it happened. Thanks for the advice though. I think you and I are right! Just replace the battery and hope that solves it.

Fortunately the car is a lease through work so it'll get replaced by them.

These batteries are tiny, it's essentially to engage the system as opposed to start the car.

If you search any Toyota forums it's a known thing.

As others have said it's been depleted too much, needs replacing. (We have a Yaris cross hybrid hence knowing a bit about them)

I think Toyota's own advice to keep them charged is, if doing short journey and say being pulled up at the shops waiting for the Mrs. Keep the car in Ready not turned off. As this helps keep the 12v charged.

People on the forums have mini solar panels on side window to keep them charged !

dirtychinchilla · 18 Mar 2025 at 13:46

Manbatius said:
These batteries are tiny, it's essentially to engage the system as opposed to start the car.

If you search any Toyota forums it's a known thing.

As others have said it's been depleted too much, needs replacing. (We have a Yaris cross hybrid hence knowing a bit about them)

I think Toyota's own advice to keep them charged is, if doing short journey and say being pulled up at the shops waiting for the Mrs. Keep the car in Ready not turned off. As this helps keep the 12v charged.

People on the forums have mini solar panels on side window to keep them charged !

Thanks! The car doesn't actually have this ready mode people are mentioning on the forums.