Failed to start... again

[pauly58]

For the second time in a month, the car had a flat  12v battery, showing 8v to be exact. Nothing obviously left on but had to get Honda Assist out to start it. I'm taking in to the dealer on Wednesday to get it checked, also the handbrake seized on last week, had a right job moving it.

At the moment the Toyota Yaris 1999 on our drive looks the better bet, never failed in 15 years.

When we got the Jazz started the radio came on & the climate control, even though the start button was in the off position when the car was last used & nothing on. It was last used on Saturday for a fairly short journey with lights, wipers etc on, does anyone know what voltage the battery charges at when loaded ? I know a conventional alternator would put in 14v when under load.

[Kremmen]

When I had a voltmeter plugged in the charging rate was 14.5v, just like a conventional alternator.

It sounds to me like your 12v battery needs a good, long, trickle charge from something like a CTEK. Batteries that become very discharged can be damaged and automatically discharge very quickly, even overnight.

Had that happen to me on a new Austin Metro. Even though the battery was only months old it became flat when she left the sidelights on and 8t refused to hold a charge, even after a 200 mile run.

[Neil Ives]

I know it's been said before; the modern so called 'intelligent' chargers are dumb when it comes to a completely flat battery*. I had to buy a second hand conventional charger for my motorbike battery when it became completety discharged.

*I think they must need to know what voltage the battery should be charged at.

[5thcivic]

Same here, many intelligent fully protected modern digital switching chargers will not charge the battery if it is too low, 6-8V for example. I still have an old analogue transformer charger which will revive a low battery enough after half an hour to enable my modern chargers to work.

[John Ratsey]

However, the fundamental question is what caused the battery to become dead in a few days? There have been a few reports of Mk 3 HR-Vs with flat batteries after being left for a week but my 2020 Crosstar had substantial periods of inactivity in my first year of ownership without any problems although I gave the 12V battery a precautionary charge every few weeks.

[Jazzik]

Our 2021 Jazz has also had substantial periods of inactivity in its first year of life, has never seen a battery charger up close and always starts without any problems.

[aphybrid]

My Crosstar has been left for up to 14 days at airport with no sign of battery deterioration/difficulty to start.

Seems silly to ask but has car always been left in P mode?

[Kremmen]

Once the battery has fully charged, 14 days is no problem.

If you collect new and don't give it a good run, or charge, to top it up, it can easily run down.

As I've said before, if I leave mine > 14 days then CTEK takes 5 or 6 hours to fully charge. Getting CTEK to stage 3, 80% charge is quick, it's the 80% to 100% that takes hours as it really is a trickle once it gets to stage 4.

[Neil Ives]

Seems silly to ask but has car always been left in P mode?

I thought you could not turn the car off if it's not in Park?

[Kremmen]

Yup, caught me out a few times

[PaultheManc]

Went on 6 week holiday in Aug/Sept with Mk4 parked in garage - started first time with no problems on return.

[mitchelln]

I was told by Honda that there is no alternator on the MK4's and it's the high voltage battery that charges up the 12V battery via a DC-DC charger.

[Kremmen]

I wonder how the HV battery is charged if no alternator of sorts ?

[mitchelln]

I wonder how the HV battery is charged if no alternator of sorts ?

It's charged by the 2nd electric motor acting as a generator coupled to the engine. Saves extra mechanical complication and a belt.

[Jazzik]

e:HEV explained: