Connecting two RC batteries in sequence is a typical follow to extend the voltage output. That is achieved by connecting the constructive terminal of 1 battery to the adverse terminal of the opposite battery, after which connecting the remaining constructive and adverse terminals to the circuit. The voltage output of the 2 batteries will probably be additive, which means that two 3.7v batteries related in sequence will produce a voltage output of seven.4v.
There are a number of advantages to connecting RC batteries in sequence. First, it could actually enhance the voltage output of the batteries, which will be needed for powering high-power units. Second, it could actually lengthen the runtime of the batteries, as the whole capability of the batteries will probably be elevated. Third, it could actually assist to stability the load on the batteries, as the present draw will probably be evenly distributed between the 2 batteries.