battery charging problem

[jackobian]

i have two battery full charged. but the amazing shocked problem when i connect them in series the polarity is reversed + becomes - and - becomes +. and when i check every one alone the polarity ok . i have not seen such a thing ever could you help me please.

 

[Audioguru]

Two batteries in series have the (-) terminal of one connected to the (+) terminal of the other. Then the unconnected (-) terminal is still negative and the unconnected (+) terminal is still positive but at double the voltage.