The use of small scale resistance projection welding may provide a cost effective alternative to manufacture battery and capacitor cover assemblies.  This article, featured in "Battery Power Magazine" reviews the various resistance projection weld methods and the benefits they provide over traditional spot welding.  The project weld technique is then applied to joining a titanium ball to a battery cover's fill port.
Reprint of Battery Power Magazine Feature Article

Resistance seam welding is a simple process that uses one or two wheels to apply pressure to the surface of conductive material. As the wheels roll, electric energy is applied using a weld controller in precise amounts. The resistance seam weld process is a fast, reliable and low cost way to join many materials. This article explores the joint types and the common configurations to used form seam welds on small scale parts.
Resistance Seam Weld Configurations

A simple and scalable means to collect, store, and analyze weld data from Miyachi Unitek’s MM‐370A and MM‐380A weld checkers (i.e. monitors) was needed. The addition of the techMatrix WeldWorksTM Software allows manufacturers to easily upload data gathered from weld monitors and controllers across the enterprise.
Using WeldWorks to Collect Data

Today’s resistance weld equipment – both small scale and large scale ‐ often incorporate integrated monitoring sensors (current, voltage, force, and displacement) that provide real‐time process feedback during the weld cycle. Like all measurement devices, weld power supplies and heads must be regularly calibrated to ensure the welder meets manufacturer’s specifications.
Resistance Welder Calibration