Battery issues in BMWs have been a common complaint among many owners. The main issue in the past was a large sleep mode demand on the battery around 40 milli amps. Today’s battery demand in sleep mode is 22 milli amps, plus the amount of time it takes for the vehicle to get to sleep mode has been reduced in comparison to older vehicles.
With such a large demand in sleep mode it took a lot of energy to replace what was lost during sleep mode and when starting the vehicle back up. Let’s go through the different battery types and common issues that cause early battery failure or the dreaded battery charge low message. I will also describe what you can do to get the most life out of your battery.
BMW uses many different types of batteries including lead acid, AGM (absorbent glass mat), and lithium ion. Each of these types of batteries have different pros and cons.
- Lead acid batteries
BMW no longer uses lead acid batteries regularly and AGM has become the standard.
-Pros: Lead acid batteries are inexpensive compared to the others. They can withstand harsh environments. They can be 100 recycled if properly done.
-Cons: they are heavy and have a short life span. Also, they self draw higher than the other two types of batteries.
2. AGM (absorbent glass mat batteries)
AGM is the most common battery in BMWs these days. Most of the new BMWs are using two batteries to assist with the electrical demand of the vehicle; especially when MSA (engine start stop system) is in use.
-Pros: longer life span, lighter weight. They also have low self discharge.
-Cons: more expensive and damaged easier when completely discharged.
3. Lithium ion
Lithium ion is the newest type of battery in BMWs. The use of Lithium ion started with the F80 M3.
-Pros: the lithium ion energy density is very high compared to the other batteries. They output of the battery is the same all the way until dead. They have the lowest self discharge rate. They will also hold a charge longer period of time.
-Cons: they are really expensive to replace. The charge rate is very specific, for example; using the wrong charger could damage the battery. The internal cells of the battery need to be monitored for temperature and charge for safety reason. If a lithium ion battery overheats it can ignite and would be very hard to extinguish.
These different batteries are marked on the case for what type they are. Once you determine what type of battery you have, then begin a care plan around the type. I witness my customer’s issues when they experience the battery discharged message in the car. There are multiple reasons this light appears. (For more, see my other post about energy diagnosis for lights turned on)
Below are other reasons why the battery drains:
- Short tripping the vehicle
Short tripping the vehicle happens whenever the energy used to start the vehicle doesn’t get replaced. Basically, if you start the car and drive 1 or 2 miles to the grocery store and shut the vehicle off; the amount of energy to start the vehicle never was replaced properly. You can see how these short excursions can add up if this is all the vehicle is used for. Of course, this is magnified in colder weather when its typically harder to charge batteries.
- 2. Long vehicle immobilization
That is a very German description of letting a car sit too long. I see this often with vehicles that are stored or are rarely driven.
3. Weather
This is the biggest issue that accentuates the other two issues listed above . Where I am, in the midwest, during the Winter months the temps can drop into the negative degrees often. These harsh temperatures makes charging a battery back up much more difficult. If you have a lead acid battery, they can completely freeze and explode under certain conditions. Lithium ion and AGM batteries can’t charge/ discharge properly when super cold or overheated.
You’re probably wondering, what can I do to help keep my battery in the best shape and get the best life out of it?
The first thing to do is analyze how you use the vehicle. Does the vehicle get short tripped a lot? Is the vehicle a secondary vehicle that doesn’t get used much?
If the vehicle is short tripped a lot, you can take a long drive every so often to keep the battery up. The other option is to use a trickle charger. A trickle charger will maintain the battery by using the low and slow method. You will want to use a smart trickle charger that can sense the battery charge level and adjust its charge rate. This is the best method to help keep the battery at full charge. A trickle charger will not recharge a very low/dead battery. BMW actually has a very nice trickle charger kit now (The old brick looking one had major issues). The kit comes with two different hook ups. One is quick clips and a version that can be hard wired. Both of these have quick connectors to connect to the charger. DO NOT connect the trickle charger directly to the battery terminals on modern vehicle because you could damage the IBS (intelligent battery sensor). Instead, put the cables on the jump post under the hood. The BMW trickle charger has two settings: one for AGM and one for Lithium ion. The newer BMWs can have a AGM battery and a smaller Lithium ion battery. When charging a dual battery system, just set the trickle charger to AGM. The lithium ion battery has its own module that regulates voltage coming into the cells and can switch it self off once fully charged.
Another item to check is the age of the battery. BMW will stamp the manufacture date of the battery on the negative post. The top two numbers are the week the battery was produced and the bottom in the year (see picture below). Lead acid will normally last 4 years. AGM will last around 5-7 years. Lithium ion will set a faults when it is at end of life. If you are close to these timelines and trickle charging isn’t helping it may be time to replace the battery. ( If you are replacing a battery please read smart charging post about registering your battery)
BMW batteries are expensive and my hope is with better understanding of proper maintenance, BMW owners can avoid early and costly replacements.
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