There are several types of batteries of various sizes and shapes. General information on batteries can be found at the following web site. Link to Batteries Batteries in series add to increase voltage of the battery pack. Batteries in parallel increase the amount of power that can be delivered by the battery pack. This is illustrated in the EWB file - Batteries.
Batteries have internal resistance.
This can be thought of as a physical resistance in series with the battery. The resistance is generally low compared to the load, but as load resistance decreases, the effect of the battery's internal resistance increases. This can be seen in this EWB file - BatteryIR.EWB . DC can be produced from AC as is done in almost every electronic device. AC to a lower voltage 2.