Hi Sam, BMW;s are good cars that go on forever (well almost), I personally would keep the BMW, once you have the problems are sorted, you will be glad that you kept it. Corolla is a reliable car, 1.6 engine, not much power, boring interior and drive, the money you would use to buy this could buy a battery etc for the BMW, end of the day has to be your choice. Not knowing too much about your personal life, but you say that you are going to be classified disabled, you could get a Motability car if you get the higher rate of disability allowance, you could get a brand new car every 3 years, insurance, servicing and no road tax to pay as rated disabled, good luck mate.