Battery Charging - Advice

[martincfreeman]

Advice needed as I am not sure if something is not right… I recently had a new battery after the dreaded “low battery please start engine message” (despite it being on a Ctek trickle charger).

I took the car off charge with the Ctek showing green / fully charged. Drove 40 miles. The car stood for a day and I then drove 40 miles back ( with a petrol stop in the middle). I put the Ctek back on straight away and 7 hours later it is still charging (stage 2 < 80%).

Surely the battery should have been fully charged after 40 miles (1hour of driving), is there a bigger problem?

Advice / experience gratefully received.

[martincfreeman]

I forgot to add, the battery was supplied and fitted by JLR assist.

[scm]

I'm not convinced the battery can really be fully charged just by driving (I'm willing to be corrected by someone who actually knows!). I've read that it takes a 20 minute drive to put back what cold starting takes out of the battery, so in your hour of driving you've actually only been adding charge for 40 minutes while also taking some out for running the car and for restarting after your petrol stop. I usually charge my car overnight when it's been a while since it's been fully charged, and it's always showing green the following morning.

[WShudds]

RPM matters more than journey time. Unless you're hitting 3K RPMs you're not really doing a great deal of recharging while driving.

[scm]

My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?

[MikeM]

Advice needed as I am not sure if something is not right… I recently had a new battery after the dreaded “low battery please start engine message” (despite it being on a Ctek trickle charger).

I took the car off charge with the Ctek showing green / fully charged. Drove 40 miles. The car stood for a day and I then drove 40 miles back ( with a petrol stop in the middle). I put the Ctek back on straight away and 7 hours later it is still charging (stage 2 < 80%).

Surely the battery should have been fully charged after 40 miles (1hour of driving), is there a bigger problem?

Advice / experience gratefully received.

From Ctek FAQ

7. My charger never goes further than the float (first green) level.

The charger stays in float maintenance mode for 10 days, keeping the battery topped up using the minimum level of current. After 10 days, the program moves on to the last stage – pulse level – for long term maintenance.

[martincfreeman]

Thanks everyone, it is encouraging that it may be that the battery was not fully charged by the drive. The journey was pretty slow so apart from a couple of quick accelerations, it was ticking over for most of the journey.

I took the battery off charge last night as wanted to get my thoughts together, and have put it back on this morning, will see how long it takes to move past the initial charge stage, It is only the 0.8 charger so really used as a maintenance over winter.

Once again, thanks for that, it is good to have a great community to get advice from.

[gasgas]

forget the charger and get it out on the road for a few hours

[cj10jeeper]

My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?

No believe this is correct even for alternators which produce effective voltage but limited current at low rpm.

Alternators will happily be providing a small charge at as little as 1000 rpm , but it’ll be almost entirely consumed by the huge swathe of electronics, displays, spark plugs, gearbox, etc. etc. before even considering incidental use such as audio, opening windows, etc. etc. and recovering from the huge drain of starting.
It’s usually considered to take in the region of 500 miles at constant high speed to charge a 50% battery.
Secondly alternators don’t charge a battery fully, rather they reduce and maintain the charge somewhere below full for the safety of electronics.

You can charge on a ctek overnight and it might be back to a decent charge, but not full. That could take much longer, so in this case charging again after slow driving will leave the ctek with plenty of work to do to complete its work.

[WShudds]

My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?

No believe this is correct even for alternators which produce effective voltage but limited current at low rpm.

Alternators will happily be providing a small charge at as little as 1000 rpm , but it’ll be almost entirely consumed by the huge swathe of electronics, displays, spark plugs, gearbox, etc. etc. before even considering incidental use such as audio, opening windows, etc. etc. and recovering from the huge drain of starting.
It’s usually considered to take in the region of 500 miles at constant high speed to charge a 50% battery.
Secondly alternators don’t charge a battery fully, rather they reduce and maintain the charge somewhere below full for the safety of electronics.

You can charge on a ctek overnight and it might be back to a decent charge, but not full. That could take much longer, so in this case charging again after slow driving will leave the ctek with plenty of work to do to complete its work.

Just to add to this, you might be able to recharge the battery faster at lower engine speeds if most electronics, headlight, AC, radio, etc are off. Do like Audi and BMW drivers and don't you dare using your indicators either!