NOVELTY - The method comprises: placing ends of copper part (1) and aluminum part (2) that are to be assembled so that the parts face one another; pressing the ends against one another so as to constitute a welding zone (3) extending along a line between the parts; applying an aluminum alloy to the welding zone by a filler metal, where the parts are held in such a way to maintain the welding zone at top using a fixing unit comprising two rigid blocks; and allowing the blocks to be held against the parts using a pressure fixing system.    USE - The method is useful for assembling a thin copper part and a thin aluminum part of electrode tabs in battery cells using heterogeneous welding (all claimed), where the battery cells are used in an electric accumulator of a light vehicle, hybrid electric vehicle and urban freight vehicle.    ADVANTAGE - The method is capable of reducing the weight and the final dimensions of the batteries, while maintaining ability of the batteries to withstand vibration.    DETAILED DESCRIPTION - The method comprises: placing ends of copper part (1) and aluminum part (2) that are to be assembled so that the parts face one another; pressing the ends against one another so as to constitute a welding zone (3) extending along a line between the parts; applying an aluminum alloy to the welding zone by a filler metal using a low energy welding method in which an electric arc (4) and a meltable filler wire (5) are wider than the combined thickness of the parts, where the parts are held in such a way to maintain the welding zone at top using a fixing unit comprising two rigid blocks made of a conductive material having thickness of 1-2 mm; and allowing the blocks to be held against the parts using a pressure fixing system. A length of the conductive material is greater than that of the parts to be welded, and the width of the material is sufficient to hold the parts. The meltable filler wire is moved vertically or obliquely downwards to the welding zone at a speed 2 m/min in the electric arc. The electric arc is produced by a metal inert gas (MIG) torch moving along the welding zone. The MIG torch implements an inert gas comprising argon. The parts are plates having a thickness of 0.1-0.5 mm. The process is controlled by a robot. INDEPENDENT CLAIMS are included for:    (1) an apparatus for performing the method; and    (2) a method for manufacturing a single cell for a battery.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a method for welding electrode tabs of battery cells.    Copper part (1)    Aluminum part (2)    Welding zone (3)    Electric arc (4)    Meltable filler wire. (5)