Car Battery – loosing charge

My Merc E-class e220d 2019 plate gets used maybe two times a week at the minute. When it is used the journeys are long ie 1hr + . However on the phone app it says the battery is now only  ‘partially charged’.

When I bought the car from Mercedes they replaced the battery as stop/start wasnt working and the battery status was worse than it is now. Merc said these cars do eat batteries if the cars are not used regularly.

I googled the cost of batteries, which was frightening ie £300 for a battery! Plus it looks a pain in the arse to fit. ie not just undo a couple of bolts.

So should I get a battery charger? Can I just get a simple £20 one? Or do I need to spend considerably more money? ie something like a CTEK. Also some online reviews I read said that not all chargers are created equally and the Merc battery requires a charge that can do 80Ah, yet I cant see where this is stipulated anywhere on specs for charges.

Ta

If it’s going flat in a couple of days after a decent run, then there’s something wrong with the battery, alternator or some part of the charging system. Take it to a garage or auto electrician for a proper diagnosis.

Edit – probably something wrong with…

But I’d still get it properly checked in just in case it leaves you stranded.

80Ah is the capacity. Ampere hours, so if you had say a 1 amp charger it’ll take 80 hours empty to full (ish), 5 amp ,16 hours, etc. Slow charge is better than fast if you have time and it won’t be empty to full. A cheap simple one is fine. You can also get solar ones that you leave in the car to keep it topped up but I’ve never tried one.

That said I’d look for other issues as to why it is going flat. Dodgy door switch leaving a light on, badly wired stereo, etc. Might just be a tired battery or a faulty alternator. These can be tested

How old is the battery?

Anything over 4 years is a bonus (even for one warrantied for 5 years)

If it’s stop-start the battery will probably be AGM which is why it’s pricier than you might expect, though the OEM spec one for my BMW wasn’t too painful at £120ish. Make sure the charger can accommodate AGM, not all of them at the cheap end of the market can and AGM charging behaviour is a bit different to a flooded battery.

I got one like this recently when my ancient Optimate died. Works well, our “big car” can go weeks between uses so I just set a reminder to plug it in every 6 weeks or so. Always worth having one anyway IMO. If the battery charges OK and shows as healthy then you can start looking at other possible causes.

https://www.amazon.co.uk/Automatic-Maintainer-Suitable-Motorcycle-Batteries/dp/B09FKXHW2R/

Yup, was about to say if it’s AGM then don’t just bung a cheap charger on it.
CTEK are tried and tested. I leave my car (with an AGM battery) plugged in all the time. Problem is once they drain fully, more often than not they’re terminally knackered.

However, losing charge on that time does possibly imply electrical fault, but I’ve no idea where to start on a car that new! It is worth considering what the parameters for it being ‘partially charged’ are though. It may just mean ‘not completely full’.

Hmm just had interesting conversations with Merc dealers, the one I purchased the car from and the one I took it to get work done at.

I am sure that when they both saw the age of the car, and the fact that I dont get it serviced there, neither of them gave a sh!t, to the point of both being rude.  Both garages could see they had done work on the car, but their records didnt show what work other than that work was done on certain days . WTF ??

From what I can recall the battery had to have been replaced in 2022, so the battery would still be under warranty.

Anyhow raised as a complaint with Merc UK.

Will take the car to the local garage who do all the servicing now as they said they will do a free check on it.

Do batteries have a manufacture date on them? I am a bit concerned they didnt replace the battery, just charged it

So after removing bits of plastic and an air filter, this is the battery…

Any ideas which is the date stamp? Also after a bit of googling it might not be as expensive as I first thought.

Edit: Answered my own question, the battery was manufactured in Jan 2022

On the negative terminal – 04 22.

April 2022 manufacture date

22nd Feb 2022?

So after removing bits of plastic and an air filter, this is the battery…

Lucky you….. I replaced the battery on my Cayenne and I had to remove the passenger seat!

Anyway – my battery lasted 11 years (and wasn’t completely screwed), so replacing a battery after 3 years is rubbish and  I’d expect something is going on or it’s just a poor electrical system!

On the negative terminal – 04 22.

Ahhh. Didn’t notice that.

(Edit: 04 can’t be the month as my old battery is 21 12 ….. maybe it’s the week number?)

Date stamp could be the 04 22 on the battery terminal, though I’ve not seen one there before. See if it seems tally to when it may have been fitted.

Some times it’s a sticker with a bit removed, stamped on the side somewhere like the hold down tab.

If you fit a new battery it may need coding (BMWs do) to the car so the car knows it’s new and it will manage the charging etc correctly.

On the negative terminal – 04 22.

Hmm I didnt see that, but used the numbers scribed in to the top right of the battery – 237 . A YouTube vid showed a table of codes that linked it to Jan 2022

Which ever way, the battery was certainly replaced by Merc in 2022 even though currently they cannot find their own record. Question is if I have to take it back to Merc now the bill could get expensive, or should they solve any issues as I raised it when I bought the car from them and they just replaced the battery?

Which ever way the battery is quite new, which is concerning why is already depleted.

If you fit a new battery it may need coding (BMWs do) to the car so the car knows it’s new and it will manage the charging etc correctly.

Yep thats why I dont want to start messing about with it myself. I know when the battery was replaced, everything in the car had reset

Doesn’t look too difficult to replace the battery yourself now that you’ve mastered taking the obscuring parts off.

Assuming the battery replacement is still called for, it should now be a matter of buying a new one from the likes of Tayna for £160ish and then re-coding via an OBD tool & phone app (widely available).

Put it on a charger for a bit. I was surprised how long it takes to recharge a car battery while driving – the AGM in my old Volvo was only partially recharged after a 5 hour motorway drive when I accidentally drained it by leaving a door ajar.

FlaperonFull Member
Put it on a charger for a bit. I was surprised how long it takes to recharge a car battery while driving – the AGM in my old Volvo was only partially recharged after a 5 hour motorway drive when I accidentally drained it by leaving a door ajar.

Especially as a lot of cars now have ‘smart’ alternators that only charge it the absolute bare minimum and only charge it up more than that under certain conditions e.g. when coasting and the ambient temperature is over X degrees and the engine is warm and … etc

Especially as a lot of cars now have ‘smart’ alternators that only charge it the absolute bare minimum and only charge it up more than that under certain conditions

Thats a fair point I drive it in ‘eco’ which means it automatically cuts the engine when coasting (or at least sets the engine to idle) . I am out this evening so I will just leave it in comfort and see if that makes any difference.

That’s an AGM ( it says so on it!) so it’s designed to take a high charge rate, which is what makes it suitable for the crank/charge cycles of a stop-start, and it’s also tolerant of being taken down to a low charge state.

It has the same cca and ah rating as the one Tayna sold me for about £120 so get your ruler out and measure it up – you can definitely do better than £300.

None of which explains why it’s only lasted 2 years, that’s really not on.

Anything over 4 years is a bonus (even for one warrantied for 5 years)

people have low expectations.

even driving cars traditionally plagued with electrical issues id be kicking shit if i had batteries that only lasted 4 years.

the berlingos on 9 years the 108s on 8 years and the campers on 15 years.

Watch me buy three new batteries this winter after writing that out 😀

A 1h+  journey twice a week should cause no problem at all for battery.    It’s usually a problem when there are weeks between journeys, not days.

Check the alternator is producing the correct voltage, you should see around 14v.

Check there is not any unexpected current draw when the car is turned off.  Lots of guides on YouTube how to do this.

You can try charging the battery outside of the car.   Once charged disconnect the charge and leave the battery to stand for a couple of hours and then check with a multi-meter the voltage across the terminals you should see at least 12.5v.

As I said earlier, you need to find out what ‘partially charged’ means in the app before you go any further imo.
Don’t rely on that, stick a meter across the terminals to see what it’s reading.

Also, has it been drained to completely flat (eg barely even cranks) at any point?

thinking more about this – if the cars got an app and so is always live – itll be caning your battery over periods of inactivity.

You can try charging the battery outside of the car.

Before you do this check that you’re not going to lose anything (head unit codes, etc.) before disconnecting.  Probs not but jIC!

Did a bit of googling on the eco v comfort thing and found someone with the same car had had the same issue.

So drove there and back in comfort rather than the regular ‘eco’’ and now the battery shows ‘Charged’ as a status. The engine is definitely starting quicker.

So my none scientific test is that if you Hsve a Merc 220d don’t drive everywhere in eco

Still find it mighty odd that Merc have no record of fitting a battery roughly 2 years ago. Thats a bit worrying. Also the way 2 dealerships involved spoke to me it’s clear they don’t give a shit unless you drive one of their brand new shiny cars

the berlingos on 9 years the 108s on 8 years and the campers on 15 years.

You’re blessed; my last two managed just about five years (Varta and whatever Kia fit OEM)

If this winter’s a cold one then be prepared 🙂

Did a bit of googling on the eco v comfort thing…

BMWs in eco mode use “Brake Energy Regeneration” rather then engine power to charge the battery. I wonder if this limits charging? Does Merc use something similar?

BMWs in eco mode use “Brake Energy Regeneration” rather then engine power to charge the battery. I wonder if this limits charging? Does Merc use something similar?

Isnt that mild hybrid technology or whatever its called to tick a box?  This is a 2019 car before all that BS came in. From what I can tell eco on this Merc really reduces throttle response, cuts the engine to idle when coasting, and clearly doesnt waste energy recharging the battery.

Also the lesson learned is that my journeys are often to football matches with Jnr FD. At arrival I will sit in the car for 45mins-1hr while they warm up. Even with the engine off most of the display is still lit up. I still managed 50.5mpg in comfort yesterday and that wasnt driving slowly so may just leave in comfort from now on

Future return journeys will now be in comfort.

My old BMW 330e did that brake thing, but it never added even 1% of charge, I cant see how it can do.

At arrival I will sit in the car for 45mins-1hr while they warm up. Even with the engine off most of the display is still lit up.

My car will switch the head unit off after about 5 mins if the engine is off due to the power draw – they can be quite power hungry.

If theres a big difference in fuel consumption between eco and comfort, then I would think, only one of your journeys needs to be in comfort to recharge the battery; you shouldn’t need every journey to recharge the battery.