As you have learned, the battery can be a big hit on points. Use the bonus points to make up the difference as they are a lot cheaper to obtain. Keep tabs on the other areas of the car which can loose points and make improvements there.
That's just how the game works at the MCA.
As for tires, my guess they thought it would be too difficult to keep track of which tires came of various models. Brands and models of tires seem to change every 6-12 months. Frankly, any reproduction tire would not pass as an original due to DOT markings.