Car Battery Drain and the Chargers to Save You

If you have followed any of my recent writing you will know I put out two significant articles about my BMW E92 M3. The first was the road to purchasing it and the second when I had severe engine failure. Well I also had another small issue occur; the increased battery discharge error message.

Always something

I have never really had to deal with a draining battery as I have mostly driven new cars and I drive them every day. Due to my current position, I have the luxury of being able to work from home multiple days a week, so the M3 just sits on those days.

Outside my home office window, so I can watch it of course.

My first battery discharge message occurred over the Memorial Day weekend. Usually when the M3 sits, it only sits for 2 days max, but with the holiday and my work from home schedule it sat for 4 days. When I finally started the M3 up, BAM. Increased battery discharge error.


Naturally, I freak out and not having a battery charger I call my father in law who is a mechanic by trade.

He lets me borrow a “god only knows the name of” brand battery charger. It charges to 100% but the battery drops to about a 25% charge soon after disconnecting. Time for a new battery.

I did some research about what battery to put in my M3 and determined it does not really matter which brand goes in as long as it is the same type (AGM) and the same size. The kicker is E9X M3’s require you to register the battery to the car, or other issues can occur. I decided to go with an AutoZone Duralast battery and registering it would be no problem since I have already picked up a Carly BMW ODBII adapter and the Android app to diagnose my previous engine failure.

Looking into battery chargers

Ideally, learning from this experience I wanted to look into battery chargers and find out which are the best. I also wanted to educate others on which battery chargers are the best, which brings us here today.

When it comes to things I do I need to find out more information on in the car world, I generally look to what I would call my “car ecosystem”. The automotive experts, car YouTube channels, etc. for reviews on cars and car related products.

When I was googling “battery chargers” I was also listening to Matt Farah’s The Smoking Tire podcast. From following Matt and listening to him weekly on his podcast I know he takes care of an ever changing fleet of cars. So he has to have an opinion on a great option for a battery charger. Why not ask him?

This isn’t the first time I have asked Matt oddball automotive questions, I inquired about some car culture suggestions for a possible cross country road trip I want to do for an upcoming vacation. So, via the Tweeter webs, Matt told me he uses a fleet of battery chargers to take care of his cars; specifically two Optima 400 chargers and two Optima 1200 chargers.


Great, Optima Batteries I have heard of them. I did further research and it appeared that his suggestion was a pretty solid one. However, I figured if I am going to educate others on battery chargers I want to see what else is out there. It is great to have one recommended option, but I figured I could put this research to good use and last thing I want to do is sound like an advertisement rather than a source of information.

Here, Buy This, One of Us, One of Us. See, sounds dumb.

After further research, I found another top recommended battery charger brand, CTEK. I determined that CTEK is the Brembo of battery chargers. They make the official OEM battery charger for pretty much every performance automotive brand including BMW, Lamborghini, Audi, among many others. In fact, many OEM chargers just replace the CTEK branding with their respective brand image.

Found the best brands, time to test the chargers

After researching which battery charger brands are recommended most, I decided to reach out to marketing reps from both CTEK and Optima to arrange some long term testing.

CTEK sent me their most advanced, and popular product, the MUS 4.3 Test & Charge along with accessories; Optima sent me their Optima 400 charger which is not their top tier charger but most comparable to the offerings of other battery charger maker type companies. Optima’s top tier is the aforementioned Optima 1200 and is the size of a small tool box and in my opinion, this baby is more usefule for when the battery is out of the car or perfect for moving around on a garage cart.

I put the chargers through multiple tests and multiple uses such as my charging my BMW E92 M3, charging a Dodge RAM 2500, charging a Ducati, charging a few ATV’s, even charging a taken-too-far-beyond-its-life Marine battery used to jump start a lawn mower. We’re nothing if not thorough here at RFD.


CTEK MUS 4.3 Test & Charge

The CTEK MUS 4.3 Test & Charge retails for $88.99. The CTEK charger has many accessory options, such as multiple “comfort” connection adapters, indicator adapters, and even a rubber bumper accessory (which was my personal favorite accessory).

Another accessory which sets CTEK apart is its “Batter Sense” accessory. Basically, you attach the Battery Sense dongle to your battery, download the CTEK phone application, and you can connect to the Battery Sense dongle via Bluetooth and track your battery charge status via your phone. As of now this is third party, but you will begin to see this in more and more cars as we go toward electric vehicles. The BMW i8, for example, currently allows battery charge status via a phone application.

Using the CTEK charger, I found it best to put the charger in my engine bay.


Early on I mentioned not having much prior knowledge of battery chargers or batteries overall. Well, one small perk I liked about the CTEK charger was the bag that is provided to hold the charger has a diagram attached showing you what order to connect what to what. The little things.




Crazy amounts of accessories No definite idea of your charge only a range
Phone application to check charge status Cannot buy in local car stores
OEM charger for many brands  

Optima Batteries 400

The Optima Batteries 400 retails for $109.99. Using the Optima 400, I found I liked to do the opposite method that I used with the CTEK charger and I liked to leave the charger outside of the car. The Optima 400 has an extremely long clamp cord, the wires that run from the device to the clamps in the engine bay or on the battery.


The Optima 400 features a small analog screen which gives text information such as “Maintaining 12V Large Battery” and also shows the battery voltage and the current amps the battery is receiving. Above the screen is a semi-circle which can be illuminated from 0-100% depending on the batteries charge level.



Visible charge from 0-100% No accessories
Analog information screen  
Can drive down to local car store to purchase  

Last words

Both chargers survived being cooked in the sun at near 100 degree weather while charging, which I do not recommend, but this was a test.

There was not one time the chargers did not do their jobs.

I was going to do some sort of giveaway for the one I did not want, but after extensive use in multiple vehicles, I am really unsure which one I like more than the other. Both have their small differences, and I wonder if the brands realize how close their products are to each other. The CTEK has great accessories, including a cool phone app, to make it incredibly easy to use, but isn’t as available to nearby stores if you need on in a pinch. The Optima is a bit more analog, but consistently got the job done, and you can go grab one at the local parts store.

It is like Pepsi and Coca Cola. You cannot go wrong with either product if you need a charger.

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