Mostly for testing purposes, systems may require DC sources. These sources may have different levels from 1.5 V to some hundreds of volts. The easiest way for creating a DC source is using commercial batteries. There are variety of batteries with different voltage levels such as 1.5 V or 9 V. In my application, I needed a nearly 100V DC source for charging a capacitor. For this purpose, I cascaded ten 9 V batteries in a form as figure below so that I could measure 96.55 V using a multimeter.
Figure 1: 96.55 V DC supply with battery stack
Due to the shape and terminal structure of 9V alkaline batteries, we can form a rigid stack of batteries for getting a different levels of DC source. One can easily obtain DC sources in a discrete levels of 9.6 volts since a fully charged battery has 9.6 V. One of the most important thing with this stack is that it has dangerous voltage levels while the count of batteries getting increasing. However, also note that each battery has internal resistance so the current that can be supplied through batteries is limited. In other words, the DC source is very useful but it has limited power due to internal resistance.
The batteries can be supplied from the links below.