Re: the open applications are consuming battery?
Were you asking about how switching between apps without terminating them affects your battery life? If this was your question, then yes; not exiting apps and leaving them in the background will consume more battery power than if they were exited completely.
Apps left in the background (non-terminated apps) have to be kept in the RAM (or at least a portion of them); the more apps that are left in the background, the more data is needed to maintain* them in RAM - "maintain" since power is needed to keep the information in RAM - once the power is shut-off the information disappears; more data means more power needed for the RAM.
But as to how much "more" power is consumed, there may be no definite evaluation since this may vary across devices and the operating conditions of the device. However, as a general practice, it is better to exit apps that are not intended to be accessed anytime soon presumably to conserve battery power.