2012 Hyundai elantra touring: Car never had problem starting. Yesterday came out to car and cd that was in player was ejected. Tried to start car - nothing. Not knowing any better, thought I needed a boost. We hooked up charger and immediately battery showed 90% charge. Took charger off, car started right away. One headlight was out, but when I started to drive away, one of the two bulbs in headlight came on. Could this be a bad ground for headlights? I should add that up to this time, check engine light was on for months (known problem - air in gas line); once the above occurred, the check engine light out, abs light on. When I shut car off and restarted, abs light out.