How to Charge BMW Battery [Full Guide]

Today we’ll take a look at how to charge a 12V battery in your BMW. You’ll also learn how the BMW battery charging process is different from conventional systems. 

Let’s get started. 

Where to Connect The Trickle Charger?

If your BMW is equipped with a lead-acid or AGM battery in combination with an intelligent battery sensor (IBS), you must connect the trickle charger at the jump-start terminal points in the engine bay. 

This way the IBS will recognize the charging. If you charge the battery directly at battery terminals or removed it from the car, this could lead to misinterpretation of the battery condition or unwanted check control messages and fault memory entries. 

For BMWs with lithium-ion 12V batteries, you can use both jump-start terminals and battery leads. BMWs with lithium-ion batteries use built-in battery electronics instead of intelligent battery sensors (IBS). 

Forget The Cigarette Lighter Socket

The 12V charging socket is supplied with voltage by the power distribution box via relay. This relay drops out after the ignition is turned off. This means that the trickle charger will be disconnected from the battery. 

Which Battery Charger to Use? 

Theoretically, you can use any 12V automotive battery charger, but I strongly recommend using a trickle charger. If you are willing to invest some $150-200 for a battery charger, look no further than CTEK MUS4.3 Test&Charge. 

Pay attention when charging a lithium-ion battery! The charging voltage generated by standard chargers for lead-acid or AGM batteries is too high for the lithium-ion battery. 

If you want a charger for both normal and lithium-ion batteries, I recommend going with a BMW Accessory Battery Charger (made by CTEK for BMW). The price is about the same as CTEK.

How Long Does it Take to Charge a Battery? 

This solely depends on the battery state of charge (SoC) and size (Ah). For most BMW batteries (80-110Ah) charging an empty battery will take about 20 to 30 hours with a 4-6 ampere charger. To boost the battery enough to start the engine will take about 4-6 hours. 

Charging The Battery While Driving 

If you’re considering charging the battery enough to start the engine, and then let the alternator do its job, do it only as the last option. Some people think they can just jump-start a car and drive around to recharge the battery, but it doesn’t work this way. 

In most cases, the alternator will only add a surface charge to the battery. That means you’ll be able to restart the engine only for a limited time, like 10 to 20 minutes after you’ve turned off the engine. And after a few hours, the battery will be dead again. 

The batteries’ main purpose is to start the engine and then work as an electrical load balancer.

So, if you need to recharge the battery, do it with a charger. 

Intelligent Alternator Control (IGR)

To make the engines more efficient and prolong the battery life, most modern BMWs (2005+) use intelligent alternator control (IGR). This means the alternator charges the battery based on a complex algorithm. In simplified terms, that means that the alternator is charging the battery only when the engine doesn’t consume fuel. 

Here’s how it works. 

The IGR is a part of the Advanced Power Management (APM) in BMW cars with internal combustion engines. The APM system has three main objectives:

  1. Save fuel (up to 3%)
  2. Prolong battery life 
  3. Secure the engine start

For this strategy to work, the alternator no longer fully charges the battery because a fully charged battery cannot accept any more energy. 

Here are three phases in which IGR operates depending on the battery state of charge:

  1. IGR Low

The IGR-Low phase starts when the battery state of charge drops below SOC_S1 (state of charge, stage 1). The IGR increases the alternator voltage during the overrun (coasting) phases. The battery charge level increases with an increased number of coastings and their duration. The state of charge can reach 100% during the IGR-Low phase. 

  1. IGR Medium

This is the sweet spot – when the battery state of charge is between about 70 – 80% (between SOC stage 1 and stage 2). During the IGR-Medium phase, the alternator only maintains the battery at this level. 

  1. IGR High

In this phase, the battery is discharged and partially supports the vehicle’s electrical system. 

So, after you fully charge the battery, your BMW will start at the IGR_High phase and slowly drain the battery to IGR_Medium. And that’s the best way to do it. 

Georg Meier

BMW technician since 1996. I began my automotive journey in 1993 as an apprentice mechanic at Automag, the world's oldest BMW dealership in Munich. With years of experience and dedication, I garnered a wealth of knowledge about the intricacies of BMW and MINI vehicles. The love/hate relationship with the brand led me to found BIMMERIST where I share expertise and insights with fellow enthusiasts.

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  • Georg, I have just discovered your wonderful web site. I was searching for information on how to properly charge my 2020 X5 (G05) and found your article. My X5 is equipped with both an AMG main battery and a Li-ion aux battery. My car does not show any battery faults but it will not load the latest software update from BMW. The car tells me it will let me know when it will be ready to install. So far I have tried all of BMW’s suggestions but it still won’t load. I’ve been told it’s probably the battery that is preventing the upgrade. So I installed my CTEK MULTI US 7002 charger overnight. I then checked the battery with my battery tester and it says it’s at 100% My question is when I connect the charger at the jump-start terminals what prevents it from charging the Li-ion battery at its higher voltage? Since I already have the CTek 7200 I don’t want to spend more money on the BMW model. Instead I guess I’ll buy CTEK LITHIUM US charger. Do I hook it up at the jump-start terminals as well? If so, does it send its lower power to the AMG battery at the same time? Will that harm the AMG battery? Another question how do I test the Li-ion battery? Does it need to be disconnected?
    Thank you in advance, your article on the battery system was the best I ‘ve found on the web. I look forward to following your web site in the future.

  • Thanks for your kind words, Mark. Yes, the main battery SOC is preventing the remote software upgrade for sure. Replacing the battery will solve the issue, but the main problem is the fault memory entry (DTC) preventing the sw upgrade, not the battery itself. The battery SoC or SoH was low at some point and the DTC (usually “aged or worn battery”) will not clear by itself even when the battery is brought back to life 100%. I’ve faced this issue many times and I can only tell you what works for me: deleting fault code entries.

    But, here’s the funny thing. You cannot delete DTCs until you replace the battery. When the OTA software updates become a reality, we were actually replacing the “good” batteries, but then I tried just to register the battery replacement without actually replacing the battery and it worked. And it worked in 100% of the cases ever since.

    The G05 can have various battery system setups depending on the model – ICE, mild hybrid (48V), or hybrid (45e), but the main 12V battery is the most important part of the system and the only one you need to take care of as a user – via jump start points. So, in your case, first, try to delete DTCs, if that doesn’t work (for me it never worked) register a battery replacement and clear the fault memory. For me, this works always. As for the charging, the lower power will not harm the AGM battery. For testing the Li-Ion batteries there’s no substitute for the BMW ISTA application as far as I’m concerned. The best way to charge the Li-ion battery is when it’s connected. Hope this helps.

    • Georg

      Thank you for getting back to me. This software upgrade problem is driving me crazy. I am not an experienced BMW mechanic so most of what you talked about in your reply is a little over my head. I attached my scanner and it returned several faults, non of which I recognized, I didn’t see any that were related to the battery. Also I’ve never seen an “aged or worn battery message” or fault. The car runs fine. I was tempted to clear the faults I did see but since I really don’t know what they mean I was unsure if I should try clearing them. There are so many different modules in the car I’m not sure what they all control.
      Now are you telling me to re-register the battery that’s in the car now? What date should I use, if I register the battery won’t the car think it’s a new battery and charge it differently ? I’ve never registered a battery so I’m not sure of all the information it requires. Also you say to clear any DTC’s related to the battery, well I really don’t see any. As you can read I’m very confused. The car is a 2020 X5 6 cylinder ICE engine and AWD. Your help I greatly appreciated.

      • Georg

        Thanks again for your reply. I’m sure my last reply has you a little confused. Today I rescanned the car and it show a few faults. I cleared them this time and re-scanned. This time I got three faults. One was the BDC or body domain controller. This one is for a steering wheel fault, it won’t work in the Longitudinal direction. This one is correct. The steering wheel will not move in and out, only up and down.
        The second fault was FZD or something to do with the sunroof. Don’t know why I got this one. We never use the sunroof.
        The last fault was very interesting. Hu-H headhunt High. Fault says “Remote software upgrade Vehicle-end Pre-conditions not fulfilled” The explanations says check energy reserve of battery. So just as you said it does look like it’s the battery’s fault the car won’t upgrade. So I guess I should try doing what you suggested, re- register the battery. Again I’m confused by this. What data should I use to register? What date? I guess I am supposed to use the data from the old battery? Won’t doing this tell the car that a new battery has been installed? Aren’t the charging methods different on a new battery as an old one?
        I will tell you this is a VERY stupid problem BMW has created. There is nothing wrong with my current battery and if the only fix is to replace it or scam the system that’s unacceptable. As you must know a new battery is damn costly.
        I hope this post makes some sense and I thank you again for all your knowledge and help. I wish I would have found this website long ago.
        P.S. I took some pictures of the faults I scanned and I was going to attach them to this replay but I don’t see how. If you would like to see them you can answer my email address and I will send them to you that way.
        Thanks again.

  • For a BMW OEM AGM battery (mine is SKU 61-21-2-353-813 80ah, 800 CCA), should the CTEK charger be set in the normal mode (14.4V) or the snowflake mode (14.7V)?

    I asked CTEK and they said “probably” 14.7V but that I should ask BMW. I asked BMW dealers (service and parts departments) and the answer came back that it is “safer” to charge in normal mode (14.4V) but they couldn’t provide a recommendation even though they sell a “BMW” CTEK smart charger. I tried the BMW “Genius” line and they just never answer. There is nothing specific in the BMW manual. I asked in the BMW dealer parts department and they couldn’t provide any specs for charging (they also said 14.4V is “safer”).

    The CTEK manual says that the snowflake mode is for charging at low temps (below 41F) and for “power” AGM batteries like Optima and Odyssey. It also says that normal mode is for “many AGM batteries”.

    I have yet to find any specific documentation on the battery from VARTA or BMW.

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