Question for BMW Roadside Assistance FreeCall, Number, BMW on Call

Our BMW 320 has been on trickle charge for several months , but at some point the charger failed to maintain the charge and now the battery is completely flat. Changing the charger does not seem to help - could the battery itself be faulty ? Would it be incorrect to jump start the car (I am concerned that all computers are shut down and so would not want to damage anything) ?