Welding on car

I picked up a bumper kit for my 2019 Renegade. The instructions have you tack it together on the car, then pull it off for finishing. They don't mention any sort of precautions to keep the computers safe. Is disconnecting the battery good enough or does something more need to be done?

I've never disconnected a computer or a battery.  Maybe I'm living dangerously but I have never had a problem.   Disconnecting the battery on a modern car creates problems all by itself so I avoid it whenever possible.

I always do ground to what I am welding on or as close to it as possible.

No guarantees this is correct, but this is just my experience. 

I've disconnected the battery and clamped the ground as close to the weld as possible in most cases, mainly exhaust or exhaust hangers with no adverse effects.

I had to use the welder on the Grand Cherokee to remove an exhaust manifold bolt that broke off on the passenger side. When doing that one I had the battery disconnected for other work, unplugged the ecu, and the TIPM was already disconnected and out. 

The main reason I unplugged the ecu is that it's mounted on the passenger fender and grounded on the passenger side of the engine. I also couldn't get the ground lead for the welder clamped close to the bolt, and the jeep was in jackstand and not insulated from earth by the tires. 

I normally unplug the battery and ground the welder as close to the weld as possible. Shorten that ground path as much as possible. 

Thanks, I wasn't looking forward to looking for and disconnecting everything for what should be a fairly quick project 

Its really only an issue if AC welding (TIG aluminum) or if during any sort of other welding you somehow ground thru another circuit.

Ive welded on thousands of cars.  Yet to ever cause an issue.

If in doubt there's always oxy-acetylene.

I always disconnect the battery because the fix (if required) is much harder.

Like RacetruckRon, my approach is to always disconnect the battery and ground as close as possible to the weld. It's an easy precautionary measure and much cheaper than frying an ECU.