There could be a couple reasons why your battery continues to be too weak to start the car. Here is just a few:

- Old battery incapable of holding charge any longer
- Alternator isn't putting out enough Amps to recharge battery
- Low Water level in battery
- Corrosion

Those are just a few I can think of off the top of my head. But there is one that from what I have seen not too many people know of.

It is know as Surface discharge. It is when excessive dirt and/or corrosion has built up on the battery giving current a path to ground from the positive terminal. It is simple to check for.

Take your Voltmeter and connect the positive lead to the positive terminal on the battery (making sure you are set to read DC Volt). Then take the negative lead and place it in a bunch of random spots all over the case of the battery. The spec for this is 0.0 DCV. I have personally seen batteries with almost 11 DCV of discharge. This could drain your battery in hours.

The correction for this is to clean the battery. Remove it completely from the car, and get a mixture of water and baking soda and carefully clean the battery all over. Let dry, clean your posts and reinstall. Perform test again and check to meet spec.

Hope this helps someone!