Put it this way, is is cheaper to replace the battery and see if it's fixed or pay a monkey to tell you your car is f*&T! Replace the battery first. Mine went, it was the original motorcraft on a 98 to be expected. Sometimes the batteries get tired and need to be replaced. I would start there if your voltage is low after start. It doesn't necessarily mean that your alternator isn't trying to charge the battery, it may be that your battery isn't just taking the charge. Cheap fix and diagnosis. Hope this helps.
