From Newsgroup: uk.d-i-y

Chris Holmes <chrispvholmes@gmail.com> wrote:

A cautionary talerCa

I had to jump start my wiferCOs hybrid Toyota before she could drive away from camp recently (we had both left our car doors open at various times,
but my dirty diesel started fine).

And even after rCLstartingrCY it (the petrol engine didnrCOt start, but it said
it was ready to drive), she still couldnrCOt go anywhere as the handbrake wouldnrCOt release automagically when she pressed the go pedal, eventually worked out she had to push / pull the handbrake switch).

I was disappointed that a nearly new car didnrCOt gracefully shutdown and restart rather than throwing a hissy fit, and also disappointed that having rCLstarted itrCY it didnrCOt just behave normally (though I suppose either / both
was better than it releasing the handbrake, putting itself in neutral and rolling downhill into the lake).

Regular (non-'mild') hybrids have their 12V battery as essentially an
accessory battery to power the electronics and ancillaries (lights, radio, wipers). On starting it has to move the high voltage battery contactors
to de-isolate the traction battery. This can take a big gulp of current,
which a nearly-flat battery can't provide. Hence the lights come on but it refuses to 'start' - you don't hear the contactors click.

When you 'jump' them, all you're doing is assisting the existing battery in smoothing out the voltage dip when those contactors take their big gulp of current - but the accessory battery doesn't get to take much charge in those few seconds. The high voltage traction system is now live and starting to charge the 12V but if you remove the 'jump' battery you're now depending on
the flat accessory battery again.

I don't know the electronic handbrake systems but it's possible it uses the
12V not the traction supply. You removed the jump battery before it had a chance to disengage the handbrake, which took more power than your flat 12V could manage. Later on, the 12V was being charged from the traction system
and had received some charge so there was a bit more charge available so the 12V could manage it.

As you say, a 'graceful' shutdown is not to just disengage the handbrake and call it a day - but you do need battery power to disengage it. When the battery is flat there's not much it can do.

I replaced my Prius 12V OEM battery with an AGM one from a UPS, which is
much better able to handle the low states of charge it gets when it doesn't
get driven for long runs and so the 12V gradually runs flat (the charging system only gives it 4A so you need to drive for hours to recharge it
fully).

Theo
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From Newsgroup: uk.d-i-y

On 21 Aug 2025 14:41:21 +0100 (BST), Theo
<theom+news@chiark.greenend.org.uk> wrote:

I replaced my Prius 12V OEM battery with an AGM one from a UPS, which is
much better able to handle the low states of charge it gets when it doesn't >get driven for long runs and so the 12V gradually runs flat (the charging >system only gives it 4A so you need to drive for hours to recharge it
fully).

I had a Prius during the pandemic and had to call the AA twice,
because the battery had gone flat and I hadn't been out much.
Afterwards, coincientally, the dealership emailed offering small solar
panels that would trickle charge the battery. Knowing that whatever
they were offering wouldn't be cheap I went on Amazon and bought one
for about u20. Coincidence or nor, I don't know, but I haven't had a
flat battery since.
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From Newsgroup: uk.d-i-y

Peter Johnson <peter@parksidewood.nospam> wrote:

On 21 Aug 2025 14:41:21 +0100 (BST), Theo
<theom+news@chiark.greenend.org.uk> wrote:

I replaced my Prius 12V OEM battery with an AGM one from a UPS, which is >much better able to handle the low states of charge it gets when it doesn't >get driven for long runs and so the 12V gradually runs flat (the charging >system only gives it 4A so you need to drive for hours to recharge it >fully).

I had a Prius during the pandemic and had to call the AA twice,
because the battery had gone flat and I hadn't been out much.
Afterwards, coincientally, the dealership emailed offering small solar
panels that would trickle charge the battery. Knowing that whatever
they were offering wouldn't be cheap I went on Amazon and bought one
for about -u20. Coincidence or nor, I don't know, but I haven't had a
flat battery since.

That will likely help a little, especially if you are also driving it regularly. On mine I set up a solar panel to fit in the quarterlight.
Problem was the 'solar charge controller' I was using would take more
current than the solar was generating and flattening the battery further.

Seems it was possibly the 5V regulator dragging it down, it was one of these trashy units:
https://www.youtube.com/watch?v=Ezh0ylkAyTw

Nowadays I just wait until the 12V gets low (months) and then put in on
charge for 24h (with a Lidl 4A smart charger) to top it back up. Being a
UPS battery it's used to that kind of cycling.

Theo
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From Newsgroup: uk.d-i-y

On Thu, 21 Aug 2025 17:19:12 +0100, Peter Johnson wrote:

On 21 Aug 2025 14:41:21 +0100 (BST), Theo
<theom+news@chiark.greenend.org.uk> wrote:

I replaced my Prius 12V OEM battery with an AGM one from a UPS, which is >>much better able to handle the low states of charge it gets when it
doesn't get driven for long runs and so the 12V gradually runs flat (the >>charging system only gives it 4A so you need to drive for hours to
recharge it fully).

I had a Prius during the pandemic and had to call the AA twice, because
the battery had gone flat and I hadn't been out much. Afterwards, coincientally, the dealership emailed offering small solar panels that
would trickle charge the battery. Knowing that whatever they were
offering wouldn't be cheap I went on Amazon and bought one for about
-u20. Coincidence or nor, I don't know, but I haven't had a flat battery since.

I used one even before the hybrid, as my use of the car was intermittent.
That was after the pandemic when it went completely flat!

I now have a hybrid (same model of car though) and the battery is wedged
into the rear wing and of course tiny. The touch locks on all but the
driver's door are shut down if the battery is low.

It was noticeable aftter a week of hot weather (and the panel facing south because of where the car had been parked) that the locks started to work!
--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me -u1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor
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From Newsgroup: uk.d-i-y

Chris Holmes <chrispvholmes@gmail.com> wrote:

A cautionary talerCa

I had to jump start my wiferCOs hybrid Toyota before she could drive away from camp recently (we had both left our car doors open at various times,
but my dirty diesel started fine).

And even after rCLstartingrCY it (the petrol engine didnrCOt start, but it said
it was ready to drive), she still couldnrCOt go anywhere as the handbrake wouldnrCOt release automagically when she pressed the go pedal, eventually worked out she had to push / pull the handbrake switch).

I was disappointed that a nearly new car didnrCOt gracefully shutdown and restart rather than throwing a hissy fit, and also disappointed that having rCLstarted itrCY it didnrCOt just behave normally (though I suppose either / both
was better than it releasing the handbrake, putting itself in neutral and rolling downhill into the lake).

I had an Outlander hybrid. Every day at 2pm, it checked if it had been
driven in the previous 24 hrs and, if not, it would rCytop uprCO the 12v battery using the drive battery and an onboard 12v charger. I could leave
it for 6 weeks at least and it would start, on electric if there was drive battery * available. I never tried longer than I recall.

I now have a Rav 4. I have yet to determine if it has a similar system.
If it has, I canrCOt find a reference to it. The drive battery is larger - just over 50 miles on a good day. For local trips, we rarely use petrol. Toyotas are great but their handbooks less so.

*hybrids start on their drive batteries and keep a rCyreserverCO, even when showing 0 electric range, for this purpose. I assume, if you kept starting
and stopping the petrol engine you could consume this reserve rCarCa The 12v battery simply powers the electronics, including the locks, and things
like lights, radio, etc. It is charged by a step down charger.
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From Newsgroup: uk.d-i-y

On 24/08/2025 16:48, Brian wrote:

hybrids start on their drive batteries

I don't think this is *universally* true...be warned
--
"And if the blind lead the blind, both shall fall into the ditch".

Gospel of St. Mathew 15:14


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