Odd Battery Behaviour

[E55BOF]

The 2007 ML 63 Japanese import I recently bought had been standing for a week, with a trickle charger on it when I was in it trying to get the hang of the new head unit (still trying...), but had not been run otherwise. I went to take it over to Terry Gates last Monday to get the tailgate sorted, and the electrics were dead as a dodo - no unlocking, no lights in the clocks, key would not even turn in the ignition. I jump started it with no difficulty from the other ML, then drove it over to Harrow - about thirty-five minutes. It wasn't charged while over there while being worked on, and I picked it up on Friday. It started fine.

According to the importer they put a new battery in it, and I think that's true. The question is, would a short run of just over half an hour be enough to fully charge a flat battery, or are the electrics set up to go dead at a certain voltage to prevent the battery being completely discharged?

 

[MikeInWimbledon]

Wiser men will quote the precise numbers to you shortly, but the "rule of thumb" I've always "known" is that it takes about eight hours of driving to fill a completely flat battery to (effectively) full.

Nonsense, of course, because it'll vary from vehicle to vehicle, drive to drive, and battery to battery.

But this dismisses any idea that a half hour run (or two half hour runs) was enough to fill your battery to "full." ("Enough to start the car a second time?" Certainly)

Unanswered questions:

If you'd trickle charged the battery, why was it flat ? Or are you saying that you only trickle charged it while playing with the head unit, and not the entire week?

What's the date printed on the side of the battery which they allegedly installed?

 

[E55BOF]

Only trickle charged while I was playing with it.

The battery lives under the driver's seat, and it's a bugger to get at, so I can't check the date on it. The importer, unprompted, when I asked about the battery told me it was a bugger to get at too, especially because initially they were looking for it under the passenger seat, from which I deduce both that they Googled and found the procedure for a LHD car, and that the battery has indeed been replaced.

Why was it flat? I don't know. Terry Gates suggested that the fault with the tailgate might have caused a battery drain.

Stood overnight for eighteen hours, it was showing 12.51 volts at the charging terminals under the bonnet today, so it may be OK now. I'm keeping an eye on it...

 

[E55BOF]

Twenty-four hours later, and it's dropped to 12.44 volts. That's 0.07 volts drop; it doesn't sound a lot, but if the battery charge chart I have is correct, and 12.5 volts is 90% and 12.42 volts is 80% charged, maybe I should be at least a bit concerned...

 

[st13phil]

Twenty-four hours later, and it's dropped to 12.44 volts. That's 0.07 volts drop; it doesn't sound a lot, but if the battery charge chart I have is correct, and 12.5 volts is 90% and 12.42 volts is 80% charged, maybe I should be at least a bit concerned...

My experience with batteries is that a surface charge, e.g. your short trip over to Wayne Gates and back, will tend to dissipate fairly quickly.

I would suggest charging the battery fully and only after that see what’s going on with voltage dropping over time.

 

[SpikyMikey]

My experience with batteries is that a surface charge, e.g. your short trip over to Wayne Gates and back, will tend to dissipate fairly quickly.

I would suggest charging the battery fully and only after that see what’s going on with voltage dropping over time.

Yep, put it on a CTEK or similar until it shows fully charged, leave it overnight and see what it looks like the following day.

 

[E55BOF]

My experience with batteries is that a surface charge, e.g. your short trip over to Wayne Gates and back, will tend to dissipate fairly quickly.

I would suggest charging the battery fully and only after that see what’s going on with voltage dropping over time.

I've not known of that one before, but the Ctek has been on it for only seventy-five minutes, and it's up to Stage 7 (Float). Oddly, though, the voltmeter shows only 12.98 volts between the Ctek terminals, and the same between the charging posts, when it should be 13.5

I don't think I need to worry, though, if the battery charged up that quickly.

 

[E55BOF]

12.61 volts after standing overnight. That'll do nicely...

 

[BTB 500]

12.61 volts after standing overnight. That'll do nicely...

That sounds a little low if it's a standard wet lead/acid battery, probably OK but I'd keep an eye on it. These are the figures I use:

 

[E55BOF]

It's an AGM battery (or should be...), so actually a bit low, but there are more differing opinions on the internet than you can count about what a 100% charged battery should be at.

I was using a 12V trickle charger before, which isn't optimal for an AGM battery, and might account for the relatively low initial reading. I'll give it another little tickle with the Ctek, I think.

 

[Bobby Dazzler]

It's an AGM battery (or should be...), so actually a bit low, but there are more differing opinions on the internet than you can count about what a 100% charged battery should be at.

I was using a 12V trickle charger before, which isn't optimal for an AGM battery, and might account for the relatively low initial reading. I'll give it another little tickle with the Ctek, I think.

Does your tickle charger have an AGM mode?

 

[E55BOF]

The old (at least 30 yrs) Halfords 10 amp one I use does not, the Ctek of course does.

 

[BIGDOG]

As a jap import I would be looking very carefully for something that’s causing a parasitic drain.
I mentioned a toll reader to you previously do start with that, it might have simply had its wires cut which I understand causes problems.
Same goes for a tv tuner or such like.

Around the drivers knee area is typical. There might alarm be a button that appears to do nothing until you put a dvd n while on the move.

 

[E55BOF]

As a jap import I would be looking very carefully for something that’s causing a parasitic drain.
I mentioned a toll reader to you previously do start with that, it might have simply had its wires cut which I understand causes problems.
Same goes for a tv tuner or such like.

Around the drivers knee area is typical. There might alarm be a button that appears to do nothing until you put a dvd n while on the move.

Could be all of the above, I think. There's a card reader of some sort in the driver's knee area, the head unit has been replaced here in the UK with a modern Chinese-made one, but there's an illuminated button next to the display which was apparently there to allow the driver to play DVDs while the car was moving, there are a couple of small boxes on the dash at the base of the screen, there's an unused connection there also, there's what looks for all the world like a tiny pea bulb on a short lead coming out above the interior mirror, and it's fitted with dashcams front and rear that I haven't even looked at yet.

Where do I find an auto electrician that could get rid of all this shit?

 

[190]

Fully charged and rested (surface charge dissipated) voltage does vary with battery type and it also varies with age. My experience on anew battery is a good 12.7 volts on a standard battery and anything up to 13.0 volts on an AGM.

In both cases that voltage won't be achieved on an older battery. I have an AGM on the bike which started life at 13.0 volts but now it's down to 12.6 volts which is understandable since it's 11 years old. Obviously due for replacement soon even though it still cranks fine . My 6 year old car battery is down from 12.7 volts to 12.5 volts which probably explains why the stop start rarely works - not necessarily something I'm concerned about.

So while the fully charged and rested voltage is a good guide to the state of charge of a battery you really need to know where your battery is in it's life cycle before interpreting the standard voltage tables.

 

[BIGDOG]

Could be all of the above, I think. There's a card reader of some sort in the driver's knee area, the head unit has been replaced here in the UK with a modern Chinese-made one, but there's an illuminated button next to the display which was apparently there to allow the driver to play DVDs while the car was moving, there are a couple of small boxes on the dash at the base of the screen, there's an unused connection there also, there's what looks for all the world like a tiny pea bulb on a short lead coming out above the interior mirror, and it's fitted with dashcams front and rear that I haven't even looked at yet.

Where do I find an auto electrician that could get rid of all this shit?

I would start with a Jap car importer, many of them also have workshops and will have seen a lot of weird and wonderful electronic ‘additions’.

I’ve been told to leave this sort of thing well alone hence the 30 seconds of scolding Japanese jibber-jabber every time I switch on.

My money would be on someone inexperienced has had a go at cleaning up the redundant accessories. As you are probably aware the TV tuner is useless in the UK and the sat nav will be stuck at whatever city the car was shipped from.

Any idea who fitted the new head unit?

 

[E55BOF]

The battery is allegedly brand new, and I'm inclined to believe that. The car did not have the factory COMAND fitted when imported, so anything that went before then, I've no idea about.

The replacement head unit is UK-spec, off Amazon (JOYX - Android 14 Car Stereo Fit For Mercedes Benz ML GL W164 Class - Wireless Carplay + Android Auto - [2G+32G] - Rear Camera FREE - IPS 9 Inch 2 Din - Steering Wheel WiFi 4G DAB Fast-boot EQ BT: Amazon.co.uk: Electronics & Photo), and though I haven't had a chance to play with it much yet, radio, Bluetooth for phone calls, and music played from a USB stick seem to be fine. I doubt whoever fitted it was a pro, though.

The car is fine if used regularly, so it's not desperately urgent. Neil Braybrook (co-founder of Comand Online) will sort it out for me in due course.

 

[badgx]

I'm sure it's already checked. Check for loose battery connection and be cautious of any aftermarket gadgets plumbed into cars electric?

 

[E55BOF]

Definitely a small drain. 12.69 volts at eleven last night, 12.58 twelve hours later.

 

[ALFAitalia]

I'd say that about right....despite what the table above says I very rarely find that a battery settles as high as 12.7v....12.6v being far more mormal....so maybe it had not fully settled when you read 12.69v.

Wet batteries...


AGM batteries...