Best battery tender for BMW M5 during winter storage?

Question

Winter is coming, and I’m getting ready to put my BMW M5 away for a few months to keep it off the salt-covered roads. Since these cars are so heavy on electronics, I’m a bit worried about the battery draining or throwing codes come springtime. I know BMWs can be picky, especially if it has an AGM or Lithium-ion battery, so I want to make sure I get something reliable that won't overcharge. I’ve looked at a few CTEK models, but I’m curious what you guys are actually using. Does anyone have a specific brand or model that works perfectly with the M5's power management system? Any tips on the best connection points under the hood would also be a huge help!

pwldoqkutk · Accepted Answer

For your situation, I would suggest going with the CTEK MXS 5.0 Battery Charger and Maintainer. I've been using this exact model on my F90 M5 for three winters now, and it's basically the gold standard for these picky BMW power management systems.

BMW actually rebrands CTEK units as their official accessory, but they charge nearly double the price—the CTEK usually runs around $90-$100 and offers a specific 'Recond' mode and AGM settings that are ESSENTIAL for our cars. If your M5 has the Lithium-ion battery (check the label!), make sure to get the CTEK Lithium US 12V Charger instead.

Anyway, back to your question about connection: be careful NOT to connect directly to the battery terminals in the trunk; it can mess with the Intelligent Battery Sensor (IBS). Always use the red jump-start post and the dedicated ground hex nut under the hood. It’s safer and keeps the electronics happy. Hope this helps!

Lioplothe · Answer

Tbh I learned the hard way that you dont need to spend 'BMW tax' money to keep the M5 happy. I went through a phase where I was buying the most expensive gear, but I’ve been using the NOCO GENIUS5 for a while now and it’s basically identical in performance for way less cash. It handles both AGM and Lithium which is great if you swap cars later. One quick tip that saved me a lot of grief—always use the jump-start terminals under the hood rather than going straight to the battery in the trunk. If you bypass the IBS system by going directly to the battery posts, your car wont realize the battery’s been charged and you might get some annoying 'battery discharged' warnings even if its full. Its just a simple way to keep the electronics from getting cranky after a long sleep...

Billyjuple · Answer

Just found this thread and man, i am in the exact same boat right now with my beast! Every time winter rolls around i get that sinking feeling in my gut about the electronics throwing a fit. Last year i legit forgot to hook mine up for just two weeks and the dash lit up like a christmas tree... it was a total nightmare to clear those codes! Honestly Lioplothe is 100% right about the price gouging at the dealership. Why pay triple for a fancy sticker? I totally agree that saving those extra bucks for actual parts is way smarter than paying for a logo. It is such a struggle trying to keep these cars happy in the cold! TL;DR: Feeling the same stress, definitely avoid the BMW tax though.