Check your small user manual for replacing the battery. The gas tank has to be removed to do this.
How do you oopen the gas tank on a BMW 528i
First, you have to remove the seat. The gas tank has to come off next. It is a little tricky. There is a bolt down on the left side which needs to come out. There is a bit of a trick to removing the two gas lines. They have a quick disconnect coupler on them. It needs to be pushed in and the lines pull apart. Then just lift the tank off. You might want to install a battery tender or something similar while you have it apart. It's that damn clock that drains the battery.
The gas tank on the 2014 BMW 7-Series holds 21.1 gal..
The gas tank on the 2013 BMW X5-M holds 22.4 gal..
The gas tank on the 2004 BMW X3 holds 17.7 gal.
The gas tank on the 2011 BMW Z4 holds 14.5 gal..
The gas tank on the 2013 BMW Z4 holds 14.5 gal..
The gas tank on the 2009 BMW M5 holds 18.5 gal..
The gas tank on the 2009 BMW X6 holds 22.5 gal..
The gas tank on the 2013 BMW X6 holds 22.4 gal..
The gas tank on the 2011 BMW M3 holds 16.6 gal..
The gas tank on the 2003 BMW X5 holds 24.3 gal..