Recently my wife and I returned from a week away and the battery in my E39 M5 was totally dead. This was disappointing because the battery was less than two years old and I had charged it prior to us leaving.
The dead battery was an Interstate MTP-95R. I’ve had good experiences in the past with Interstate batteries so this was an unwelcome surprise. I tried to revive the battery with my NOCO G3500 charger but it wouldn’t hold a charge. Admittedly I’m driving both cars a lot less due to the pandemic, but this was way too early for the battery to become a paperweight.
Fortunately in the E39 M5 battery replacement is straightforward. As I talked about in my E46 battery post, these were among the last generation of BMWs that do not require “registration” of the new battery with the car’s electrical system. So there is no need to go to a dealer or purchase aftermarket software.
I decided to not only change battery brand but also battery technology. The new battery is a Duralast Diehard Platinum AGM battery. AGM stands for absorbent glass mat. It’s still a lead acid battery but the internal construction is different. Benefits include slightly higher power, resistance to vibration and (deciding factor for me) better recharging capability after discharge. Here’s detailed description and a video if you want a deep dive.
An exact fit was also important to me and the Diehard advertised the exact dimensions of the Interstate. It was very close but was not exact. I added a sponge to make the fit snug in the compartment and the battery was a little taller, despite saying it was the same 7.5 inches in height. The foam and plastic cover still fit but now sticks up slightly.
AGM sometimes costs more than conventional batteries. But in this case the Diehard was almost the same advertised price as the Interstate, and I got a 10 percent discount and core replacement refund. The battery also came with a three year replacement warranty.
AGM batteries don’t discharge as much gas as conventional but there still is some, so I reused the plastic elbow to vent the battery. Without the need for registration the only challenge with this job is picking these batteries up – they are very heavy. Remember to bend your knees.
Replacing your own battery is a good and easy introduction to DIY. My E46 battery post has strong Google juice and is a page one listing on search engine response pages. Hopefully this post will help a lot of BMW owners as well. Here’s to a better 2021 and Merry New Year!
Bad Interstate
Empty compartment – note vent hose to left
New Diehard AGM in place – see blue adjustment sponge and black elbow attachment on left top near positive terminal
Cover back on but bulging slightly
Thanks for your pictures. The issue of fitment is the vent line is not in the same location as stock, off about an inch. I noticed this also recently with Duralast H9 AGM(autozone), and had to cut a notch into the foam that secures the battery from the top to fit properly. The vent line is in the correct position with other H9 AGMs i.e. Superstart H9 AGM (Oreilly’s) or Duracell 95R AGM (batteries plus) . You can see the difference in position from your pictures. For others if you don’t want to cut the foam I recommend getting the Superstart AGM ($199 versus $289), pay attention to vent location. My last AGM Superstart platinum AGM lasted almost 5 yrs, not terrible and better than previous Autocraft Gold though its vent was also in the proper position(died in 3yrs 3 months, AdvanceAuto). I believe the Autocraft Gold battery has been rebadge as the DieHard Gold non-AGM.