Charging battery of modern car

[Edward1949]

Our Diesel Toyota Avensis has been idle during Coronavus lockdown. Never a great starter, I anticipate difficulty when the time comes to use it (unlike the Morris which bursts into life after weeks lying dormant) so I'd like to charge the battery. Internet is full of dire warnings and contradictory advice about advisability of disconnecting battery before charging modern cars.
Any thoughts? All advice gratefully received.

[Des911]

My Porsche Boxster has been on trickle charge for weeks and always starts first time after leaving on charge with no extra precautions like disconnecting the battery

[KeithL]

I've always charged my modern cars without disconnecting the battery and no obvious ill effects so far.

[geoberni]

I have a 2010 Ford Kuga, it could probably do with a new battery as it is on the original and it can fail to turn over if left for a couple of weeks and it has been known to let me down if it has several stops/starts in the space of a few minutes (long story).

I have a regular old style charger that is probably 30+ yrs old, with a simple Low/High switch on it. I just place it on charge for a day once a week on the Low setting and it's doing fine.
Diesels are more of a problem than petrol engines as they need a lot more ommph to get them going, so an older battery really shows up it's shortcomings.

[alanworland]

I understand that the most modern cars employ an ECU which monitors all charge and discharging of the battery and therefore have dedicated charging points so any additional charging can be taken into account through the ECU.

Alan

[geoberni]

I guess with 'modern car' technology advancing all the time, particularly as regards batteries, the best recommendation would be to check the owners handbook and see if there are any warnings or other cautions regarding battery charging.

[alawrence10360]

I think you only need to be careful if you are considering boost starting/ charging
I have cooked an ecu carrying this out on a Scania in the past however the voltage did reach over 36V which is the point at which most ECUs will start to alarm (18V on 12V systems )
The DC output from a charger does have an AC ripple and so the peak can be higher than the RMS value you will see on your multimeter but the average automotive charger will not cause any issues to an ecu or any other system on a modern car

[ian.mcdougall]

Hi
I would look at your drivers manual and see if it recommends how to charge battery and follow that and you can't go wrong.
Ian

[jagnut66]

(unlike the Morris which bursts into life after weeks lying dormant)

My Porsche Boxster has been on trickle charge for weeks and always starts first time after leaving on charge

Methinks (after reading the above and other posts) that not all progress is good progress and perhaps simpler is sometimes better......
Mind you I'd rather be driving the Morris anyway, so perhaps I'm bias.....
Best wishes,
Mike.

[noidea]

i had one of my cars on trickle charge over the winter no problem with battery when starting but then noticed the speedo was going back and forwards had to send it to etb instruments to have it re calibrated as it had wiped the memory was told to dissconect the battery when charging in the future
dave

[KeithL]

Dave,

That's worrying. What car was that out of interest?

[noidea]

this was on an ac cobra replica
dave

[Edward1949]

Follow-up report: yesterday we needed to use a car for the first time since lockdown. As anticipated the Morris fired up instantly and the Toyota failed to start - tried until the starter would no longer turn. Connected my 25 year-old charger (having disconnected battery earth lead from car) and kept an eye on charge rate dropping from 5 amps to 1 amp after about 6 hours. Car now starts! Very relieved to report that none of the adverse symptoms reported on Toyota forums have appeared ( eg. electric windows developing a mind of their own/ door-lock problems/ engine management issues). Phew!
One word for the Morris - "Respect!"

[SteveClem]

Recently had to put a new battery on a 2010 Tiguan, just as simple as changing a Minor battery. And the radio didn’t pack up either...