Battery Charging - Advice

M

martincfreeman

New member
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.
 
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.
 
RPM matters more than journey time. Unless you're hitting 3K RPMs you're not really doing a great deal of recharging while driving.
 
My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?
 
martincfreeman said:
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.
Click to expand...

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.
 
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.
 
scm said:
My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?
Click to expand...

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.
 
cj10jeeper said:
scm said:
My alternator produces 14.5V at tickover .... Are you sure you're not thinking of dynamos?
Click to expand...

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.
Click to expand...

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! 😊
 
Are we saying that if I leave my car sitting there idling that the battery would gradually run down because the alternator is unable to provide enough power for everything?
I'd be very surprised if that were the case. But perhaps with AC, seat cooling, headlamps etc etc.....
 
pirateprentice said:
Are we saying that if I leave my car sitting there idling that the battery would gradually run down because the alternator is unable to provide enough power for everything?
I'd be very surprised if that were the case. But perhaps with AC, seat cooling, headlamps etc etc.....
Click to expand...

Not under normal conditions as the alternator’s primary purpose is to cover the needs of the car whilst driving, and with surplus keep the battery topped. I can however imagine an extreme scenario as you describe where you ran everything in the car headlights, fans, seat heater, etc. for hours that the battery would deplete unless it’s sophisticated and increases the rpm.
 
It will not run it down but it will struggle to recover the energy used to start the engine. Do it a few times and you can run into issues and it will shorten the battery lifespan.

Besides, leaving a car idling for prolonged periods of time puts the engine through unnecessary stress and it's not recommended especially in the winter. You'll be increasing the chances of oil dilution as well due to the higher fuel concentration.
 
had my car on a ctek 5 charger/maintainer for past 7 days and charge on the bluetooth battery monitor shows it has fluctuated between 13.9 and 14.02 and the percentage on the monitor showed 100% after initial charging then disappeared
anybody know if this is normal as seems quite high, thanks
 
Dkfallon said:
had my car on a ctek 5 charger/maintainer for past 7 days and charge on the bluetooth battery monitor shows it has fluctuated between 13.9 and 14.02 and the percentage on the monitor showed 100% after initial charging then disappeared
anybody know if this is normal as seems quite high, thanks
Click to expand...

The CTEC will be giving an output of 14.4v to mid 15’s depending on circumstances, cycle, etc.. It will temporarily raise the voltage of the battery which I assume is what you’re seeing on the Bluetooth monitor. You need to wait 12 hours after charger is removed and then test to get a valid battery reading and be looking for around 12.6v
 
My CTEK MXS 5.0 handbook has a table showing the various stages of charging and the current and voltage levels used.
 
I'm not an expert in this field, but have researched this in the past thanks to battery problems with another car. From my understanding, alternators increase current output with engine RPM, but it’s not a linear relationship. At lower RPMs the alternator output drops off significantly, which potentially can lead to the kind of issues described here.

Take the F Type's V8 superxcharged engine, for example. These engines produce a lot of torque, which means they can happily keep up with motorway traffic at lower RPMs, say 1300 RPM, especially with an 8-speed gearbox.

But while the engine is running at loow RPM, the alternator isn’t able to generate as much power. On top of that, modern cars often have battery management systems (BMS) that are designed to save fuel and reduce emissions, particularly in "eco" modes. This keeps politicians happy, but not necessarily your battery - these systems sometimes limit the alternator’s output, especially when the car’s battery is already relatively charged, usually around 80%, I believe. (Again, I'm not an expert)!

Therefore at low RPMs, the alternator might not be charging the battery enough, which could leave you with an undercharged battery – especially if you’re doing a lot of low-speed driviing or long stretches in traffic.

So, even though the car can happily cruise at low RPM all day, the combination of lower alternator output and BMS restrictions can sometimes mean your battery isn't getting the charge it needs.

I hope that is helpful, and if there is an expert here, I'm happy to be corrected if I have anything wrong :)
 
I’ve had this problem with both my MY14 and MY18, unless you drive it hard you don’t end up charging the battery enough to get rid of the low battery message, coasting at low RPM or sitting still does pretty much nothing. Going from a low battery message to good charge level with ctek takes a while as ctek is designed to drip feed charge at low level for a long time hence you may still be at stage 2 after 7 hours. For reference I put ctek on recently after getting low battery message and left it a couple of hours overnight to come back to the same message in the morning however in my case it could’ve be the battery as the car still has the original battery from 7 years ago however given your battery is new then I won’t say it’s anything to worry about unless your battery starts getting drained when not connected to ctek.

Also great explanation honeybadger.
 
Yeah, when I get the low battery warning (not often, fortunately!) that's my signal the car definitely wants an overnight charge - like pretending it's an EV. And I sometimes do the overnight charge things at random times, just to keep it fully topped up.
 
You must log in or register to reply here.
Back
Top