How do u jump start BMW without being able to get to battery

Did you jump the battery backwards, positive to negative? If so you have burned out the computer modules most likely.

BMW batteries are usually under the rear seat, however there are special terminals under the hood which can also be used. It really makes little sense to work on your own car without buying a cheap shop manual, especially a BMW.

Certainly sounds like a lack of power in the battery.
Do you have a genuine BMW battery or a cheapie replacement?
Have you tried to jump start the vehicle.
Batteries can seem ok, but when called upon, the power drawn out of them can be insufficient.
Try charging battery and starting on the charger- or just jump start to see what happens

No danger involved, just useless. If ONE vehicle won't jump it, there's something drastically wrong with the engine. A charging system will only charge a max of 14 volts when charging a low or dead battery. Over that will hurt something. If you have two vehicles connected to your low battery, there's still only 14 volts going out from them and into yours. There is no reason why one jump vehicle won't charge and start your vehicle. Unless of course the jumped battery is really bad or has a bad/dirty connection. So clean your terminals before a jump. You may not need a jump.

You do not need to access the battery to jump start your 7 Series. There is a metal terminal under the hood for jump starting your car or jumping another car. It is located near the passenger at the rear and has a red cap with a PLUS symbol on it. Remove the red cap and attach the postive side of the cable. Attach the negative side to the large nut just to the left.

Also, to open your trunk manually insert the metal key in the key hole next to the button that you push above your license plate.

Good that the general electrical systems are reporting no faults but the issue sounds more fundamental. The battery probably shows 12v but if it is sick (its internal resistance will be high) it will carry low current. The starter motor demands very large current. Without the aid of the jump does the car turn over in a healthy way? If not, then go to basics and have the battery checked over, most of the 'Kwikfit' type depots and Halfords will have facilities to do this

It sounds to me like neither the battery nor the alternator is the problem. The first thing to check is the wire connections at the starter, a starter solenoid if one is used and the battery. Dead alternators never charge the battery and a car with a dead alternator will not ever start without a jump or a charge. A dying starter, if it turns over at all will draw so much current that it will kill the battery in a couple of starts. A final note - many auto parts stores can check the condition of the entire battery - charging - starting system without taking anything off the car and they will do it for free. I would check for loose wires first.

new altenator,sounds like you put the cables on the wrong way round

Pop open the hood (bonnet) on the left isde of the firewall there is a red/black battery connection so you can jump start the car without getting to the battery.

sounds like it's your alternator, your alternator charges your battery and runs car once it is started. if you have a bad alternator your battery light will come on, and shortly after your vehicle will die, unable to restart without a jump. I would take your battery to autozone or an auto shop to have your battery and alternator tested.