Question About Battery Disconnect when Welding Cat Converter Bracket

Hi all, long time lurker, first time poster.

I had my local mechanic install a Cat Security shield since I park outside. He had no issues doing that but found that one of the brackets for the catalytic converter had come off and needs to be welded back on. This makes sense as I had been hearing some rattling before the installation.

My mechanic is great but old school so he's not always confident when it comes to some things on my car. He asked me to try to figure out what precautions we'd need to take before doing any welding on the vehicle.

So my question is, what needs to be done before they weld the catalytic converter bracket?

At first I thought that he'd just need to disconnect the 12V battery and remove the service plug grip. Does the Hybrid battery, or anything else, also need to be disconnected? Does either battery or both need to be removed?

thanks! --greg