I think my battery has died young!

[BobA]

Went to church yesterday morning, car started fine. Came out and it wouldn’t start with various warnings about a low battery. Started it with a jump start and drove home, checked the battery voltage with the engine off and it was 12.5V - pretty low after just stopping the car! Put the charger on and it started off at 8.5A and after about 2 hours it had settled down to 2.5A with the battery at 13.somethingV . This morning the charger had switched off and the battery was 14.5V.

So the car’s happy again meantime but there’s no way a completely flat 100Ah battery could fully charge in such a short time at 2A - that’s less than about 40Ah, so I guess it’s died young (build date is April 2018). I got a warning about 4 months ago here: 

So I’ll need to see what battery it has. I know roughly where it is under the boot but could someone be more exact how to get to it please (2019 G31 530d)? I don’t want to fiddle about with ISTA on my PC but I’ve got Bimmercode and BimmerLink on the iPhone - I guess they’ll do the job? Any pointers to a suitable battery supplier? Thanks.

 

Edited January 23, 2023 by BobA

[mikefitz]

Your battery is either a 95 Ah AGM type 019, or a 105 Ah AGM type 020. Top choice would be the Bosch S5 or the Varta silver dynamic, ( the same battery,   different label) . Costs around £200  to £215 Inc vat and carriage  for the 105 Ah battery, a bit less for the 95Ah. Another excellent  battery is the Yuasa 105 Ah YBX9020 and the 95 Ah YBX9019.

Yuasa batteries are available from Halfords and all the on line outlets. Tayna always seem to be competitive for batteries

https://www.tayna.co.uk/car-batteries/

My guess is your battery is the 105 Ah, if not, it would be worth fitting  the larger battery.

Access is where you would expect a spare wheel, if your G31 is a anything like my F11.  My comments are for a F11 but your vehicle should be similar.

The boot floor lifts on a gas ram  revealing  a shallow trim cover over the remaining area.  This is held in place with plastic rivets  at the rear edge, use a trim tool or small screwdriver to remove these. 

First disconnect the negative terminal, 10mm spanner/socket, and put to one side. Remove the hold down plate, 13mm spanner/ socket, finally the positive  terminal and the associated distribution panel.

Replace battery and connect up in reverse order, negative last. 

Register the battery with Bimmercode/link, 'how to' on you tube.

Don't close the tail gate  with the battery disconnected.

Mike

 

[BobA]

Thanks for that, I wasn’t expecting the floor to be riveted which is why I was a bit uncertain quite where to look. Will anything be a nuisance after the battery’s been disconnected or will it just all come back up as it was before? Last time the $tealer had it it lost things like radio presets, seat memory etc. TBH although I’ve had a few BMW 5ers this is the first time I’ve had to worry about the battery even in cars substantially older!

[Procion]

Where your car leads Bob, mine seems to follow and I’m equally confused about G31 batteries.

My car seems to have two. One in the boot, the other is front passenger side under the scuttle. The scuttle battery is a 105amp hr Bosch AGM, the one in the boot I don’t know, as I haven’t opened it up to see.

I did look on Ista (slides attached) which shows a beast of a Lithium Ion battery under the bottom boot liner.  The roles of these batteries I do not understand and how long they’re supposed to last, I’ve no idea. Hopefully someone will drop by and enlighten us, or you’ll have to go a garage to find out and share the knowledge.

 

 

[Matthew]

@Procion, Yours is possibly the mild hybrid model that uses a 48v system hence the additional battery under the bonnet. 

@BobA, are you using a specific charger for AGM batteries? The battery should last for much longer than the current 4 - 5 years. The AGM in our F45 is 8,5 years old and still going strong. When I charge the battery in my G32 it doesn’t go any higher than 12.6v which is what I’d expect for a 12v battery, with the engine running it measures around 14v at the battery terminals. Have you checked for a parasitic drain?
 

 

[BobA]

13 hours ago, Matthew said:

 

@BobA, are you using a specific charger for AGM batteries? The battery should last for much longer than the current 4 - 5 years. The AGM in our F45 is 8,5 years old and still going strong. When I charge the battery in my G32 it doesn’t go any higher than 12.6v which is what I’d expect for a 12v battery, with the engine running it measures around 14v at the battery terminals. Have you checked for a parasitic drain?
 

 

Thanks for that @Matthew,

Yes, always on the AGM setting. I think 12.6 is rather low for fully charged mind you - I’d expect nearer 2.2V per cell and a bit more with a trickle input so I’d expect around 13.5V if it’s just finished topping up. I think the 14.5V on mine was because I’d just reset the charger and the battery was full (I read it off the charger screen). Read at the jump start terminals.

I think what bothers me more is how quickly it charged from flat. Mine is a nominal 8A charger but on anything except a really flat battery it usually settles nearer 2.5A and at that rate I’d expect it to take nearer 2 days to charge the battery from flat, not just 12 hours.

I’ve no idea how to check for a parasitic discharge really without disconnecting the battery and using a meter in series. I’ve not done that. This must be the first time I’ve had a battery issue in 30 years or more so I’m a bit surprised.

Edited January 30, 2023 by BobA

[Procion]

As it was a sunny Sunday I took a brave pill and opened the boot trays up. Very easy. Only need to remove the small one at the very back for inspection purposes. Lift the cover to 45' wiggle the long tongued hinges free. Lift the whole cover up above where the boot cover sits to glass height and you can get it out of the hatch easily. Lift the core pin of the single plastic rivet to the LHS of the rear lip and up she comes. Wow! Very colourful with all the cables and modules. What it all does I've not the foggiest but I sure wouldn't want to get it wet.

As you can see there is a beast of a battery (105Ah) lurking below. I assume this is the main battery for starting etc. The little fella under the bonnet (60Ah) probably keeps all the computers alive and not a lot more. How they work together, if they do, I dunno. National grid would be proud of the G30s complexity. Me? I just drive it!

 

 

[Matthew]

1 hour ago, Procion said:

As it was a sunny Sunday I took a brave pill and opened the boot trays up. Very easy. Only need to remove the small one at the very back for inspection purposes. Lift the cover to 45' wiggle the long tongued hinges free. Lift the whole cover up above where the boot cover sits to glass height and you can get it out of the hatch easily. Lift the core pin of the single plastic rivet to the LHS of the rear lip and up she comes. Wow! Very colourful with all the cables and modules. What it all does I've not the foggiest but I sure wouldn't want to get it wet.

As you can see there is a beast of a battery (105Ah) lurking below. I assume this is the main battery for starting etc. The little fella under the bonnet (60Ah) probably keeps all the computers alive and not a lot more. How they work together, if they do, I dunno. National grid would be proud of the G30s complexity. Me? I just drive it!

Both the main and auxiliary batteries support all power systems in the car and there is no discrimination between the 2. I think your car has active roll stabilisation and 4-wheel steering and both these systems have additional electrical load requirements hence the need for an additional and auxiliary battery. My G32 only has the 4-wheel steering so I just have a really small auxiliary battery alongside the main battery in the boot.

AGM batteries will last much longer than lead acid ones and the battery in our F45 is 9 years old this year, the car is really low mileage with mainly town driving and the original AGM battery is still going strong.

[Matthew]

@Procion, Looking at your picture again, you also have the small additional auxiliary battery to the left of your main battery under the boot floor. So 3 batteries in the car overall.