Get a volt meter and make sure red is on v/ohm and black cable plugged into common or ground. measure the battery. if the meter is reading a negative reading then polarity is backwards. look for a positive value of 19v +/- a volt. red will be positive. if there is 3 leads I would think the temp lead would measure different. Usually common would be the negative side.
Answers & Comments
Get a volt meter and make sure red is on v/ohm and black cable plugged into common or ground. measure the battery. if the meter is reading a negative reading then polarity is backwards. look for a positive value of 19v +/- a volt. red will be positive. if there is 3 leads I would think the temp lead would measure different. Usually common would be the negative side.