Battery polarity in battery diagrams can be confusing for those who don't understand the rules used in their drawing. Battery symbols appear on diagrams called "schematic diagrams" that show how the power flows through the circuit for the given device. Polarity of a battery symbol within a schematic diagram can be determined strictly in how the symbol appears.
Lay the schematic on your reading surface and orient it so that the side with the battery symbol is to your left.
Look closely at the battery symbol on the schematic. No matter how many cells the battery symbol has, there are two lines that tell you what the polarity is in the schematic. The two lines are on the far top and far bottom of the battery symbol, or on the far left and the far right. One line is longer and the other line is the shortest of them all. The longest top or end line is the positive (+) terminal of the battery and the shortest line is the negative (-) terminal of the battery.
Follow the voltage through the circuit schematic by following the line that intersects with the shortest line of the battery symbol, following it through the circuit until it returns to the longer positive line of the battery symbol. Current always flows from the negative polarity of the power source and returns to the power source on the positive polarity.
Some battery symbols don't appear with the long and short lines, but rather two small round circles. One circle has a "+" sign near it and the other has a "-" sign near it. A "-" sign is always the negative terminal and a "+" sign is always the positive terminal.