A smart battery charger, or trickle charger, is the one car item many of us overlook. But it’s certainly one of the first things you should have in your toolbox. I’ve recently learned that lesson with my BMW 1M Coupe. Being such a special and very limited car, my “Baby-M” doesn’t see a lot of winters and snow. So naturally, it sits in the garage. More than it should, some would argue. And that comes with a price.

Many modern BMWs pull a lot of power from their battery and if driven on mostly short trips or sit for long, will have shortened battery life. So a few days ago, I went to startup the 1M, only to find out that its battery is dead. Granted, the original factory battery has never been changed so having it last over 10 years is quite an accomplishment. But as I learned, you can further extend or even revive a battery by using a smart battery charger.

Why Do I Need A Battery Charger?

BMW-branded CTEK Battery Charger

Smart battery chargers or battery tenders will charge a battery until full and “tend” the battery. When the battery needs more power, it will cycle on and off keeping it full but not over charging it. This is opposed to they style you see at an auto parts store where they try to rapidly bring the car battery back to life but will keep charging even if the battery is full. Those are not meant to stay on a battery long.

So my research brought me to the CTEK (56-353) MULTI US 7002 12-Volt Battery Charger and the CTEK (56-959) MUS 4.3 TEST&CHARGE 12 Volt Fully Automatic Charger and Tester. Both are made a respectable brand and both come either recommended by other BMW owners or have great reviews on Amazon. 

There aren’t may differences between the two. The 56-353 has charging Amps of 0.3 to 7A, while the 56-959 delivers 0.8 to 4.3A. The first one is the more premium choice, but in the end, they both work well on my 1M. In the end, I picked the CTEK 56-959 since it was on sale. Be advised that some newer M cars use lithium ion batteries and need a charger designed for lithium batteries. Always check the manual before use.

How Does It Work

Used here on E92 M3

It’s always best to use the included manual, but this is how I’m using the CTEK on my BMW. The battery charger has alligator style clips and four different charging modes. Simply hook the charger’s red and black alligator clips up to your BMW and press the mode button to select either Motor Cycle, Automobile, Cold battery, or recondition battery.

Connect the red clip to the red power terminal and the black to the ground. One can either connect the battery charger by directly accessing the BMW’s battery through the trunk or via the engine compartment on the red power terminal and the ground.

If you don’t like to keep your hood open, you can even route the charging cables up through the bottom of the windshield and close the engine bay lid.

The Lights Meaning

On this particular unit, there are 8 LED lights. After you connect the battery charger to your BMW, the CTEK unit will cycle through the first 6 lights. When the 7th light turns green, then the BMW’s battery is fully charged and the charger goes into a maintenance mode. If the battery voltage drops, the battery charger / trickle charger will resume its operation. There is an 8th light which will light up if the battery needs a top off.

Why Do I Need One?

No one can argue that most BMW batteries are expensive. So by using a battery charger you could extend your BMW’s battery and save money in the long run. And you won’t be stranded like I was when I wanted to go for a ride.

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Can you put a battery charger on a BMW?

Yes! You can use a battery charger to either maintain the charge of your battery, precondition it or to jump start it.

How often should I charge my BMW battery?

BMW says that the BMW High Voltage Battery is designed to withstand frequent charging periods. As such, they recommend charging at least a few times per week, so that your vehicle has the maximum state of charge to operate at the highest ability possible.

Does a BMW battery need to be programmed?

All BMW models manufactured after 2002 require battery registration, as they are significantly more advanced in terms of electrical environment.

What is the lifespan of a BMW battery?

On average, a BMW battery will last three to five years.