Next Can of Worms – Chargers: CTEK, NOCO or Other?

[Best4x4xFar]

So as I have read in my research on a replacement battery for our X5, it seems that maintenance charging the battery with an external charger is recommended for a few reasons. If I am understanding correctly, one being that the car itself is designed (maybe more accurately programmed?) NOT to fully charge the battery. And this gets compounded if the vehicle is not driven enough, or for long enough on each trip. As a result, I am now down the rabbit hole of research on a charger for this purpose. I understand that AGM batteries require different charge voltages than flooded lead acid, and that it is best to have a charger that has specifically programmed modes for AGM charging. Easy enough, no shortage of these available.

CTEK comes up over and over on the BMW forums, and BMW rebrands a CTEK charger to sell it for twice the price, so it seems an obvious choice. The CTEK MS 5.0 seems to be the same charger BMW rebrands, and the CTEK MUS 4.3 also seems to have a popular following. Other than the ‘test’ functions of the MUS 4.3, the charge functions appear to be identical, both having 4.3 A Max outputs.

NOCO also has some chargers of interest, the one being most closely comparable seems to be the NOCO Genius 5, which charges at a max rate of 5 A. There is also the NOCO Genius 2D, that Charges at a max rate of 2 A. I like that both are weatherproof and designed to be ‘installed’ in the vehicle. The Genius 5 has most of the same features of the CTEK, but the 2D is a bit more basic.


The noted battery guru on Bimmerfest (yes, Doug) cautions repeatedly about not charging at more than 4 A. The CTEK he uses charges at a marginally higher rate, and the GENIUS 5 at again, marginally more. I’m not sure I understand where this warning comes from, as it is seems AGM batteries can accept charge rates much higher, and I have to assume the car itself can charge the battery at much higher rates when called for.

I would love to understand this better, but from what I can find online, it seems like the general rule of thumb seems to be to charge at about 10% (.1C) of the rated Ah capacity (about 10.5A for a 105 Ah battery), and that you can charge AGM batteries as high as 30% (.3C) of the rated Ah capacity (31.5A for a 105 Ah battery) occasionally, but not recommended to do so regularly. So throwing out the max permissible and sticking with the typically recommended 10% of Ah guideline (.1C), it seems like up to 10 A would be safe on a regular basis. So is it something in the BMW electronics that risks damage at higher rates?

I have used Deltran Battery Tenders (1.25 A) for decades now on motorcycle batteries as well as an older classic vehicle that doesn’t get out much, with great success. But they don’t seem optimized for AGM, and like they are a step behind the CTEK and NOCO offerings. Maybe there are other charges out there I should be considering as well, I dunno..

I like the idea of mounting a NOCO under the hood, permanently hooked up, so I just have to plug it into an extension cord (our X5, sadly, is not garage kept), and I am leaning toward the NOCO Genius 5, but this isn’t a requirement. I just want to get the best tool for the job. So I’m all ears everyone..

[Thecastle]

I charge my BMW v8's regularly to prolong battery life and ensure reliability. Another not talked about issue is if the battery is not charged enough, when the car is turned off it will not run the turbo cooling pumps and fans to preserve battery power. Damaging the turbos overtime.

Any charger that lists AMPS of charging is the maximum number of amps the charger can charge with if the battery will accept it generally when its lower than 80% State of Charge SOC.

When the battery gets near full i.e. the same voltage as the target voltage, the batteries will automatically pull (accept) less amps. The charges are not fixed in amp output, they are just capped. Generally the slower the charge the less heat and longer the life of the battery

With that said I have a 1.25amp Battery Tender which supports Flooded/AGM on my X5M when in storage. Works great battery lasted for years. I replace them every 4 years preventatively here in my climate. Heat kills batteries.

I also have a 4 amp Battery Tender for battery maintenance on my other cars, 550i, mini, and X3. It works fine generally tops the cars off in a few hours.

When you want more amps is if you have a big battery bank. I have a bucket truck with multiple 4D batteries. So it has a 400ah boom battery bank, if the bank was 50% depleted, you want a bigger charger so it can recharge in less than 24 hours. I use a 25ah battery charge for that one.

I use battery tender for car storage and they work great. My friend uses them on his car collection with no issues. Any good charger will work fine. The ones to watch for are the ones who don't have a float mode and continue to overcharge your batteries.

[mitch808]

I have a 1A trickle charger NOCO, a 10A NOCO, and a NOCO battery jump starter. I love their products. Charges and jumps all of my cars and scooter. AGM, lithium, 6V and standard lead-acid batteries.

In one case though, a electrical gremlin on one of my rides, the 1A trickle isn't enough. But that's a problem with the GM based car and a bad circuit somewhere with phantom power draw.

[T-Dubbs]

I used to have a large garage of cars to look after, and they all ran Ctek's(all 18 cars).

They are a premium cost, but they are the best out there from my experiences.

[135ivert]

Thanks! I was wondering why my CTEK 3300 wasn't doing the trick on my X5M. It does great, however, on my 135i, which is weird because the CTEK is for lead acid only.

I just put the NOCO Genius 10 in my cart and it should be here tomorrow.

Would it affect cranking time on the X5M? My other 3 cars startup immediately. This one seems to take a few beats.

Edit: Put the NOCO Genius 10 on the X5M in AGM mode. It showed one red bar . . .I probably don't drive it enough to keep it charged. The NOCO is heavy and seems really substantial compared to the CTEK.