just get new batteries and save the head aches and danger of adding a product other than clean water to the batteries. if those products really worked, every gas station and forklift and golf cart place would be selling them, not drugstores.
the amps go up because the batteries are bad, I am pretty sure you will see a more familiar response from the charger once good batteries are installed..
weak batteries will cause problems (wear and earlier than natural failure rates) in all the other components of the power control, including the motor and it's brushes. the money you put out for good batteries will more than equal the money you save by not having poor batteries cause added wear.