I have had a horrible time with this 2013 Malibu Eco. New brakes, rotors, caliper, belt, battery, and timing chain. Now the day after getting the timing chain fixed, the battery voltage is reading 11.4 most of the time when I'm driving it. It has entered battery saving mode twice and each time I drive it, it says "Service battery charging system". The code reader says something about the second battery in the car having the fault. How do I fix this and how much is a replacement battery? I bought the car from my brother for 3 grand and I've put 2 grand into it already. HELP!