Batteries are like opinions, everybody's got one

Batteries are like opinions, everybody's got one

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anonymous-user

Original Poster:

53 months

Wednesday 24th February 2021
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Car batteries are like opinions, everybody's got one - and more and more of them are fancy AGM batteries designed for start/stop systems etc. Meanwhile every dealership wants to sell their parts and service by saying you should only use OEM batteries and a new battery must be coded to the car at £££ + VAT.

Are car owners following this guidance or do you still buy a cheaper battery of the same type and fit it yourself? The first time I replaced an AGM was before I'd heard all this. Being fairly thorough, I checked the exact battery specification and bought an identical model. Simply removed the old one, fitted the new one and all has been fine. I'm now coming up to another AGM replacement and encountering ambitious dealer pricing (nearly £500 fitted) when similar batteries can be bought online for £160. Can't get the exact same model from the same manufacturer but a battery of identical specification is available.

I'd be interested to know if other people are replacing AGMs themselves and whether you're encountering any problems.


mwstewart

7,554 posts

187 months

Wednesday 24th February 2021
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It depends.

For the daily the OEM spec battery is absolutely fine. I generally fit Bosch S5.

The hatchback has a different requirement to stock so I have scaled up accordingly.

The Ferrari is a weight-saving project so I have scaled back to the minimum that I'm happy with for the typical temperature range in which I use the car.

anonymous-user

Original Poster:

53 months

Wednesday 24th February 2021
quotequote all
My question is more around the technology and how the systems may be affected than just buying on price.

I'm wondering whether DIYers run into any difficulties with AGM battery replacements. From my own clicking around it sounds as though it's probably important to fit a new battery of identical specification (not just one that fits, or bigger capacity for luck) but that the "coding" part of things may be less critical.

There are suggestions online that it "depends on the car". Something about a difference between open systems and closed systems which I don't understand.

Scrump

21,893 posts

157 months

Wednesday 24th February 2021
quotequote all
I have replaced two AGM batteries this winter. By coincidence both of them were on cars 6 years old.
Did both myself, batteries were not from the car manufacturer but were good quality ones with the same spec as OEM.
With both cars I maintained power to the vehicle using a spare battery, so had no problems.

Before I replaced these I checked to see if the car had to be coded to the new battery and in both cases the answer was no.
It seemed to me that BMWs are the make which is most mentioned in discussions about new batteries needing to be coded. Maybe this what you mean by open and closed systems. BMW (and others) have some sort of battery management system which needs to be told that a new battery has been fitted and what capacity it is.

mwstewart

7,554 posts

187 months

Wednesday 24th February 2021
quotequote all
I haven't heard the term open or closed but I wonder if it refers to an open/vented battery (usually lead acid) or a sealed battery (normally AGM), if so that doesn't make a huge amount of difference other than the OEM AGM car likely doesn't have provision for a vent tube.

I've run AGM and lead in the same car: they are interchangeable. Most aftermarket lithium batteries are backwards compatible, too.

anonymous-user

Original Poster:

53 months

Wednesday 24th February 2021
quotequote all
Scrump said:
I have replaced two AGM batteries this winter. By coincidence both of them were on cars 6 years old.
Did both myself, batteries were not from the car manufacturer but were good quality ones with the same spec as OEM.
With both cars I maintained power to the vehicle using a spare battery, so had no problems.
Excellent, that's the way I'm planning to do the next one and have ordered some crocodile clips to make up a lead and keep things nice and easy maintaining power.

For mwstewart - the open/closed question is, I believe, about software of the electronic charge control systems rather than battery venting.

stevemcs

8,593 posts

92 months

Wednesday 24th February 2021
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The only ones I would actively avoid are Lion, other than that my preference would be Varta, Bosch or OEM. Ford are selling Omnicraft batteries stupidly cheap at the minute and are allegedly made by Varta.

So do need coding, so don't but if yours is one of those that needs coding then get it done.

KingofKong

1,965 posts

42 months

Wednesday 24th February 2021
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I saved about £125 on my VW battery by getting my battery from a specialist supplier (and a 3 year warranty) but I had to pay £20 to get it coded by another independent specialist.

Smart alternators need to know the charging state of your battery, so replacing new for old without coding may mean your new battery is only being charged to your old batteries capacity.

anonymous-user

Original Poster:

53 months

Wednesday 24th February 2021
quotequote all
Only difficulty encountered was how heavy it was to lift out an awkward corner on a F30 BMW. The torque is specified for each nut and bolt. With many online guides no longer free I would have to pay just to find out whether the battery terminal is 10nm or 11. Coding was straight forward. It was a two part process. Registration and then programming. Thankfully the app and adapter used were an investment. BMW wanted £458 for supply, fit and, coding. I did it for £300. Purchase of the battery, app, OBD II adaptor and, a torque wrench.

Jakg

3,451 posts

167 months

Wednesday 24th February 2021
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KingofKong said:
Smart alternators need to know the charging state of your battery, so replacing new for old without coding may mean your new battery is only being charged to your old batteries capacity.
I've seen a lot of people talk about saving money by not coding / registering batteries on newer BMW's... and then saving money again by not doing it when they replace the battery quite soon afterwards!

My 335d should have an AGM battery, but I had some electrical problems where the car thought the battery was excessively discharging.
The car didn't have an AGM battery fitted, but it thought it did. And it seems likely that if that wasn't updated, it wasn't registered either.
The car started fine, and the battery didn't even look that old, but I still had to swap it. No real evidence but I reckon if it was done properly I wouldn't of been in that situation.

It's a bit of a faff, sure, but the cable for the car was a tenner and the software was free online, so it's no great hardship.

EDIT - I always buy the largest battery that fits in the OE space, in the 335d scenario I bought a Halfords AGM one which is a made by Yuasa.

anonymous-user

Original Poster:

53 months

Wednesday 24th February 2021
quotequote all
Jakg said:
I always buy the largest battery that fits in the OE space,
Yes, that's the old-fashioned approach. The question here is what actually happens if you fit a new battery of identical specification and don't get it coded.

A number of people have said, "You should get it coded". Yes, we know that. The question is what, if anything, happens if you don't get it coded.

underwhelmist

1,852 posts

133 months

Wednesday 24th February 2021
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Super_G said:
I would have to pay just to find out whether the battery terminal is 10nm or 11.
The difference between 10 Nm and 11 Nm is hardly worth bothering about is it? I bet most torque wrenches aren't that accurate. Not that I've ever used a torque wrench on a battery clamp.

Sheepshanks

32,541 posts

118 months

Wednesday 24th February 2021
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rockin said:
Yes, that's the old-fashioned approach. The question here is what actually happens if you fit a new battery of identical specification and don't get it coded.

A number of people have said, "You should get it coded". Yes, we know that. The question is what, if anything, happens if you don't get it coded.
We have a couple of VAG models in the family fleet and supposedly ( based on what I’ve read in marque forums) the ecu remembers the charging state of the battery so if you don’t erase it the car still thinks the battery is old. There’s also settings for different types of battery if it’s not replaced like for like.

MB140

4,028 posts

102 months

Thursday 25th February 2021
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I paid £140 from my local mechanic for a VARTA battery (brilliant old school guy) and £15 to fit it (BMW M135i).

As the battery is in the boot it just looked a bh to do with a load of crap on top (actually he comment on BMW cost saving by making the cables as short as possible and requiring two people to do the job as you couldn’t hold all the crap from on top of the battery and replace it at the same time.

He then charged me £5 to code it. Even suggested an app I could use to do it myself if I wanted to but at £30 I can have 6 batteries coded by him so why bother.

KingofKong

1,965 posts

42 months

Thursday 25th February 2021
quotequote all
rockin said:
A number of people have said, "You should get it coded". Yes, we know that. The question is what, if anything, happens if you don't get it coded.
I answered above.

Good article here - https://pmmonline.co.uk/technical/the-role-that-ba...

My VW has stop/start, smart alternator, regenerative breaking, event data recorder and all kinds of other electrical systems.

So my new battery has now been coded and the alternator is giving it a higher level of charge than the old battery, it peaks at 14.6v now, the battery monitor is showing it as 99% healthy and when left for a few days the voltage is sitting at 12.6v with onboard systems sleeping.

The old battery wasn’t getting that level of charge, was charging slowly, nor was it holding anything above 12v for more than a few hours.

There also a serial number tucked away in the coding, assume that’s for warranty claims and you can change the capacity in the programming too.

anonymous-user

Original Poster:

53 months

Thursday 25th February 2021
quotequote all
KingofKong said:
The old battery wasn’t getting that level of charge, was charging slowly...
Again, yes. The clever electronickery must have a "learning" ability - otherwise it would start life charging a new battery at the new battery rate and never realise that over time the battery has got older, adjusting the rate of charge accordingly.

The internet suggests that if I fit a new battery (of identical specification) and don't have it coded then all that will happen may be it takes the charging system a while to learn that the new battery is better than the old one and can be fully charged. However, the outcome may depend on the particular make of car. (There are some reports of A/C and other accessories not working at full power until the learning process has been completed although I'm unclear whether those accessories will previously have been automatically restricted to protect the old, weak battery.)

My car knows it's got a weak battery because it sometimes puts up a "battery low" warning on the dash when the car is started. Since the battery is more than 8 years old it's fair to assume the warning system is correct. The main dealer wants nearly £500 to supply, fit and code a new battery. The local marque specialist offers the same for about £350. A new battery from a reputable online supplier comes in at £160 (plus delivery).

Unless significant risks are identified I'm going to DIY it and see what happens - after which I'll be happy to report the results, either good or bad!

Sheepshanks

32,541 posts

118 months

Thursday 25th February 2021
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rockin said:
Again, yes. The clever electronickery must have a "learning" ability - otherwise it would start life charging a new battery at the new battery rate and never realise that over time the battery has got older, adjusting the rate of charge accordingly.
What I've read is that the car remembers the charging state of the battery and this memory needs to be erased. Whether it can dynamically adjust the charge pattern, I don't know, but it seems to be suggested not.


rockin said:
Unless significant risks are identified I'm going to DIY it and see what happens - after which I'll be happy to report the results, either good or bad!
As best I can gather, you won't notice any difference. The life of the new battery may be shorter - but chances are you wouldn't notice this, you might not even have the car by the time it expires.


It's usually tough to get straight answers on stuff like this - for instance no one seems to know how diesel booster heaters work or what parameters affect variable service intervals. There's lots of opinion around, but little reliable information.

KingofKong

1,965 posts

42 months

Thursday 25th February 2021
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This is a great little widget for battery monitoring -

https://www.amazon.co.uk/dp/B01MT4583U/ref=cm_sw_r...