Quote:
Originally Posted by Franko666
Now I am confused. When you read the online manual for 330i it says to charge battery from under the bonnet at the connection terminals. Should I not be charging the battery directly if the system is showing low battery?
Took the car for an hours run on Tuesday but still getting low battery. Any advice would be greatly received.
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Actually, it's all quite complicated, but can be quite simple...
Modern chargers don't just pump juice into the battery until it explodes. They check / test / recondition / pump up / lay off / trickle charge until the battery is purring along nicely. I'm sure that modern alternators do the same over extended drives, but don't quote me on this.
The challenge is that modern batteries are designed to hold and discharge vast amounts of charge and as such need special care to be kept at optimum levels. This works out just fine when you drive a 'decent distance' every few days / weeks, but anything less requires a bit of TLC.
I had a BMW 535d many years ago that only did short trips once a day - about 4 miles in total. It turned out that the drain on the battery needed to start a 3L diesel was not being replenished in a 2 mile drive to the train station, and then back again. In winter. With lights / AC and what not ablaze. After about 2 weeks and once the battery ran down, it was game over. Even permanent connection to a charger failed to resurrect that battery, but that was 15 years ago...
Modern chargers do a whole bunch of tests / conditioning tasks before actually charging / maintaining. This is good as it 'gets to know' the condition of your battery, but it does take time - probably more than an hour of driving.
Like pretty much everyone here, I have used a CTEK battery charger on my Ariel Nomad over the past 2 years: a 2.4L engine with a piddly motorbike battery that gets used 'every now and then'. Seriously, the low battery indicator light flashes when just starting the car at a full 14.8V!
The short answer: it takes time to fully inspect / charge a large AGM battery. On my Nomad, the CTEK whips through the Desulphation / Soft Start / Bulk / Absorption / Analyse / Recond / Float stages and moves on to the Pulse stage in a matter of minutes - before I can scrape all the mud out of my teeth.
What has surprised me on the M340i is that the same process takes a few hours (piddly bike battery V large boot-mounted behemoth?)
In my experience, our cars need a proper modern charger (like the CTEK cited here) connected straight onto the battery connection points under the bonnet (forget the 12V 'Output' charger and all it's diodes inside the car), left for 5 - 6 hours to get the modern AGM battery back into tip-top condition after a period of no usage.
I'm not convinced that an hour's drive can drag a 'low charge' depleted battery back into normal working order. If a modern charger drawing 240V from a home socket takes 5-6 hours to work through the various battery restoration phases, a 12V alternator on an hour's drive has a limited chance I would say.
Just my tuppence...