^ No actually, keeping frequently used programs in RAM saves the time and CPU needed to re launch them. Keeping programs in RAM doesn't eat battery, its just the CPU cycles that do. When the system needs more RAM, it automatically closes the apps that are not required.
Refer this Android Task Killers Explained: What They Do and Why You Shouldn't Use Them
Refer this Android Task Killers Explained: What They Do and Why You Shouldn't Use Them