1 Other owners recommended the Interstate MTP-91, and this is the model that I first went to obtain. The MTP-91 is slightly smaller than the factory battery and the vent tube shape and location are also different, requiring an adapter. At the auto place, the latest Interstate catalog showed the new MTP-H6 model as a direct fit replacement, while still showing the MTP-91 as an alternate fitment. Sure enough, the MTP-H6 was about as identical to the factory battery as you can get, even having the same size drain hole size and placement. To change the battery out, you will need a 10mm socket and your radio passcode.
First, loosen and remove the ground terminal. This eliminates the possibility of short circuits when you remove the positive terminal next.
2 After removing the battery terminals, use the same 10mm socket to remove the clamp at the rearward end of the battery.
3 Then, unplug the drain tube from the forward end of the battery and remove the battery by sliding it rearward and out. This photo shows how the MTP-H6 is identical in form factor to the BMW battery.
4 Install the new battery in the reverse sequence. First, you will want to roughen up and remove any oxidation from the battery terminals. You can use a special battery tool, wire brush, or simply a small piece of sandpaper. Slide the battery in and forward, then reattach and tighten the rearward clamp. Next, plug the vent tube into the hole on the forward edge of the battery. Then attach the positive terminal first, followed by the ground terminal.
5 In this photo you can see that the OEM factory cap for the positive terminal fits nicely into the mounting holes on the MTP-H6.