Help with Onan 5000 starts won’t stay running.

When the generator stops normally the indicator light blinks a pattern
Like 3-3-2 3-3-2 3-3-2 (the pattern is usually longer) Write it down and post it

Then we have a clue
Some things that can cause that
Dirty slip rings
Bad oil pressure sensor
Other bad sensors
Bad control board (The parts that read the sensors)
and so on.

But with the code we get a clue.

Dirt slip rings often report as "Cranking speed too slow or low battery" by the way.