those are both pics of the outer pads correct? if the inner pads are around the same thickness I would say you have easily at least 20,000 miles left on them.
Brake pads start out new at around 12mm and it looks like you are down to around half, maybe a bit under.
well actually it most likely only has a 30 month ( 2 1/2 Year) free replacement warranty and after that you will get a discount on a replacement battery anywhere from 10% to 50% depending on the age of the battery.
Since your battery is going on 6 years old, it is your battery for sure. Not many people know this but Home Depot sells automotive batteries and they are at a good price. I suggest getting the Exide Extreme battery, the CX-5 takes a group 35 battery, it comes with a 40 month replacement...
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1/2 qt in 500 miles doesn't seem right to me, did you wait about 10 minutes after shutting off the engine before checking the dipstick and was the vehicle on level ground both times?