Up until recently I've been getting between 23 and 28 MPG, which is pretty reasonable and expected. Trouble is, just the other day I had to call a breakdown service to replace my old worn out battery, and since then I've been dismayed to see my MPG drop to around 12 MPG even though I'm driving the same as normal. Not only that, but when I filled up for the first time since having the battery changed it was reading far more in the tank than I was expecting. The fact that the readings have been odd ever since the battery change seems too much of a coincidence. Could the change have knocked all the computers out of sync or something?