The combination of two or more electrochemical cells in a series is called a battery.

Here's why:

* Electrochemical cell: A single unit that converts chemical energy into electrical energy through redox reactions.

* Series connection: Cells are connected end-to-end, with the positive terminal of one cell connected to the negative terminal of the next. This increases the overall voltage of the system.

A battery is essentially a collection of electrochemical cells designed to provide a specific voltage and current output.