The difference of Voltage between four 1.5V batteries in series and in parallel
The voltage remain at 12V when two 12V batteries are connected in parallel; the voltage become 24V when two 12V batteries are connected in series, and the voltage is 48V when four 12V batteries are connected in series.http://www.jinhuasunrise.com/en/article/batteriesconnectedseriesandparallel.html
When the batteries are connected in series, the positive terminals should connect to the negative terminals. And when the batteries are connected in parallel, the positive terminals should connect to themselves, and the negative terminals should connect to themselves. If you want to increase the battery capacity, you should choose the connect way in parallel, and if you want to improve the battery voltage, then the connect way in series should be chose.