[Feanor]

Hi all, it's been a few years since I posted here!

I've had my 2012 F30 320d from new and have never replaced the battery. I've had a few issues with the computer complaining about drain if I left the car unused for many weeks or if I was sat in the car with the lights on in cold weather after a short run to the shops where the battery hadn't had the chance to recharge, so five years ago I bought a jump start battery just in case which I've never needed except to help others out. It still doesn't seem to miss a beat but where I am in Europe now the winters can be very cold and my daily commute only 15 minutes so I bought a CTEK charger just to reduce the wear of deep discharges and when stop/start consistently stops working consistently I just give it a charge.

I have it serviced at BMW whenever the computer recommends but they've not suggested a new battery. Bearing in mind all the computerised diagnostics this car has, surely the computer should say if the battery needs replacing?

My battery's not had an easy life: much of the time the car has been used for daily short city trips with 30-60 minute journeys every few weeks, interspersed with very long cross-continental journeys a few times a year - and it's suffered deep discharges on a number of occasions from lack of use. It's also often been parked outside in both very hot and pretty cold weather. I'm just a bit puzzled at the lack of objective information out there: all I can find is rather old school advice of waiting for issues to arise, and DIY types who replace their battery every 3/6/8 or whatever years. Based on my experience though the more frequent changes seem rather wasteful, and considering the cost of these AGM batteries, rather unnecessarily expensive - so am I just lucky in not having my computer tell me I need a new battery, or am I missing something?

[RAK92]

Not the answer to your question (sorry), but have you considered purchasing a battery tender and keeping it hooked up when the car isn’t being used? That will surely extend the life of your battery.

[Feanor]

Originally Posted by RAK92

Not the answer to your question (sorry), but have you considered purchasing a battery tender and keeping it hooked up when the car isn’t being used? That will surely extend the life of your battery.

I think the CTEK charger is supposed to switch over to that when charging is completed but I think I read somewhere that it's not good to keep AGM batteries at full charge for long periods as the battery chemistry is completely different. But to be honest I kind of gave up trying to understand all that after a very confusing email exchange with CTEK about the charger's "AGM Recond" mode which seems to be pointless as AGM batteries don't apparently need reconditioning, and indeed it sounds like it can actually be bad for them (although, granted, reconditioning is a different process to the battery being left on tender).

Tbh though it's also less that the car goes long periods without being used at all, which has only happened for max 2 weeks in the past 2-3 years, but that it gets frequent but short cold weather use where the battery doesn't really have a chance to manage more than a basic recharge in the 10-20 mins it takes me to commute at the moment. That's where topping up with my CTEK every so often helps. It also makes me feel like I'm part way to driving a plug in hybrid because the extra energy in the battery from the wall socket means the start-stop then works much more often!

[Billfitz]

The computer can't tell you if the battery is good or not. One of these can:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Where your CTEK is concerned don't wait until you have symptoms of low charge, use it pro-actively to prevent a low charge situation from occurring.

[Feanor]

Originally Posted by Billfitz

The computer can't tell you if the battery is good or not. One of these can:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Where your CTEK is concerned don't wait until you have symptoms of low charge, use it pro-actively to prevent a low charge situation from occurring.

Thanks, although that looks like it's just a straight volt meter? If so it'll only verify charge status, it won't check Wh capacity or crank amp capability. Testers are available to check crank amps etc though so I could just get one of those but I only want to do that if there's genuine value in it.

Fully agree about proactively charging, useful to hear my thoughts about that confirmed .

[Billfitz]

It is a volt meter, but configured to be more user friendly than a typical DMM. You can test cranking amps as well, but if the battery doesn't hold the minimum voltage it's just as much in need of replacement.

[Feanor]

Originally Posted by Billfitz

It is a volt meter, but configured to be more user friendly than a typical DMM. You can test cranking amps as well, but if the battery doesn't hold the minimum voltage it's just as much in need of replacement.

I'd go further than that - if the battery doesn't hold the minimum voltage then it's in much more need of replacement . I've frequently seen non-automative lead acid batteries which appear to hold voltage even for an hour or so of light use but when tested for longer periods or under load their capacity is shot as failing batteries can do funny things in terms of the rate at which their voltage drops off. Reduced cranking amps will give you much earlier signs that the battery is reaching EOL .

In terms of monitoring the car battery's voltage, tbh I'm content with using the car's willingness to activate start/stop at junctions as a proxy for whether the battery's holding voltage: when that ceases to work after either charging or a long enough drive then I'll know for sure that it's time to replace the battery. I just want to make sure that the battery won't go from the voltage appearing OK to me and the car to suddenly failing.

[HighlandPete]

Originally Posted by Feanor

I just want to make sure that the battery won't go from the voltage appearing OK to me and the car to suddenly failing.

That's the difficult one to judge. I've just replaced my 10-years old battery in the F11. Original was slowly losing the ability to charge to optimum voltage, even using the CTEK.

Changed it, as I didn't want to be caught out with a failed battery. I still need to give it a charge occasionally, as I'm not using the car enough. The new battery voltage still drops back after a few days of inactivity.

I had a car which started fine in the morning, but the battery was dead when I went to go home at lunch time. Battery had completely failed. No other clues, other than knowing the battery was a few years old.

[chowser51]

Have it load tested.

[Feanor]

Originally Posted by HighlandPete

That's the difficult one to judge. I've just replaced my 10-years old battery in the F11. Original was slowly losing the ability to charge to optimum voltage, even using the CTEK.

Changed it, as I didn't want to be caught out with a failed battery. I still need to give it a charge occasionally, as I'm not using the car enough. The new battery voltage still drops back after a few days of inactivity.

I had a car which started fine in the morning, but the battery was dead when I went to go home at lunch time. Battery had completely failed. No other clues, other than knowing the battery was a few years old.

Interesting. Curious to know what type of battery was the one that suddenly failed and what generation of vehicle it was in? And whether you ever did a crank test on it?

Personally I'd rather prepare to avoid getting stuck in that scenario by just keeping a jump start battery in the boot and some jump leads in case that doesn't work, there'll always be someone to jump off to get me home then I can buy a new battery after I get home. I find it wasteful to replace things every few years just in case when the serviceable life might be the best part of a decade, the impact of everyone doing that across all the cars on the road would be considerable not least the increase in the cost of running the car - and of all the things that might fail at least there's a short term workaround for a battery when it does go.

Originally Posted by chowser51

Have it load tested.

Yeah - I think I'll do that

[HighlandPete]

Originally Posted by Feanor

Interesting. Curious to know what type of battery was the one that suddenly failed and what generation of vehicle it was in? And whether you ever did a crank test on it?.

Wasn't a AGM... back in the days of my Rover 416 GTi. I'd not tested it or charged it before it failed, was used daily at the time. Local tyre shop tested it, dead.

[Billfitz]

Originally Posted by Feanor

In terms of monitoring the car battery's voltage, tbh I'm content with using the car's willingness to activate start/stop at junctions as a proxy for whether the battery's holding voltage

That was more or less valid before the advent of modern auto electronics, but not now. BMWs, and for that matter all but the most basic car models today, are never actually 'off'. There's always a drain on the battery. So long as the car storage conditions aren't too cold, the time between uses not too long and the trip speed and duration not too slow or short that drain won't cause a problem, but if any of those conditions exist, let alone more than one, a perfectly good battery may not have enough charge to start the car, or if it does some functions may be restricted. When that happens the knee jerk reaction is usually to replace the battery, even though it may only need proper care.

Since I live where it does get well below freezing in winter, when I tend to drive only once or twice a week, usually less than 10 miles at moderate speed, I plug in my battery maintainer most nights between December and March. This particular ounce of prevention is worth quite a few pounds of cure.

[Heel328]

The original battery in my old 1995 Audi S6 was still working after 17 years when I sold it. I'm still on my original 2013 328i battery. I don't expect it to last 17 years but hoping for 10 or so..

[Fliplegend]

If you read enough battery threads on here, you should feel fortunate to have yours last 7+ years.

[Billfitz]

If you believed batteries need replacing as often as some say they do you'd keep a spare on hand.

[Desertnate]

Lifespan of a battery seems to be a gamble based on so many different variables already mentioned.

One thing I've noticed lately is batteries don't seem to give any signs of starting to fail like they used to. In the past, slow starting was a good sign the battery was starting to go dead, and if you paid attention you'd be able to catch it pretty early. The last two batteries I've had to replace (in totally different cars) failed suddenly with no warning at all. One start it turns over just fine, the very next time...nothing... The only common denominator was age of about 4~6 years.

When I hit the 4~5 year point on a battery I start to get nervous, especially when headed into winter.

[LeshiL]

There is a grandfatherly way to check the battery. If the car is not set, measure the voltage of the device, it should be 12.5 volts approximately. On the started car, if the voltage is more than 14.5 volts, then the battery is bad. And battery sellers have a device: a load plug. Can show the battery status more accurately

[Billfitz]

When the car is running you're not reading the battery voltage, you're reading the alternator output voltage. If it's higher than 14.5v that may indicate a bad voltage regulator, which can result in battery over-charging and eventual battery failure.

[CajunBMW]

Originally Posted by Billfitz

The computer can't tell you if the battery is good or not. One of these can:
https://www.amazon.com/gp/product/B0...UTF8&psc=1

Where your CTEK is concerned don't wait until you have symptoms of low charge, use it pro-actively to prevent a low charge situation from occurring.

Do just keep this plugged in? Or would you use it for a couple of days on one car and then move it around to see how each is doing? It looks like a solid item and if I buy one I just was wondering if I would get one for each vehicle or just use one and move it around.
Thanks

[Gen13 F36]

Sure , the computer indicate by stop functioning then your stranded in the middle of no where.

[Billfitz]

Originally Posted by CajunBMW

Do just keep this plugged in? Or would you use it for a couple of days on one car and then move it around to see how each is doing?

You could do that, but in Louisiana you shouldn't need to use one unless you've got a car that you're not going to drive for at least a week. I'm religious about using mine in winter, because I only drive one day a week for a short distance and the temperature can go for weeks without going above 30 degrees. In summer I drive more often and don't plug it in at all.

[heifetz17]

The car doesn't necessarily tell you when the battery needs to be replaced, but it will tell you if it has a consistently low charge. That warning is what triggered me to test my original battery and ultimately replace it. However, I rely heavily on battery critical features such as the parallel parking lights and parked car ventilation, so I need my battery to be strong at all times.