My battery got no more energy, but i don't know where it is. My car is bmw 1990 735iL.
Please help me ...

It is inside the Fuse Box.

No, it's not inside the fuse box. It's under the back seat. However, located under the back seat IS a second fusebox, known as the Rear Power Distribution Box.

Removing the battery:

0) Make sure you know your radio code!

1) Pry off the little plastic cover located on the rear seat on the passenger side.

2) Using a 10mm socket, remove another little plastic cover under the first one.

3) Using a 13mm socket, disconnect the negative lead of the battery at the place provided-it's obvious.

4) Lift straight up on the rear seat and viola, there is the battery. The thing on the driver's side is the rear power distribution center. Notice it actually has some fuses, so this would be a good time to make sure all of the fuses are OK. It's also a good time to collect all of those coins and ink pens that have fallen out of passenger's pockets over the years, not to mention finding the source of that yucky smell you sometimes get a whiff of :-), just kidding I hope.

5) After you put the seat back together, enter the radio code so the radio works again.

A couple of other notes. The battery for a BMW 7-series is big and heavy. For some reason, weird electrical things happen (like the false transmission error) when the voltage is low, so get the right battery. Translation: it'll be expensive as far as batteries go.

Also, it's in the passenger cabin with you and it has a plastic vent tube to give the ???fumes??? from the battery a place to go besides inside the cabin with you. When you remove the battery, notice carefully where this vent tube goes so you can put it back in the same place.

Thank you so much. I know what i have to do. thank you for your help