I have an 08 E350 SD cutaway with Utility body and 4WD conversion with 6.0 Powerstroke engine. The battery light is coming on intermittently, sometimes every few minutes and sometimes not for an hour or more. It has new batteries and the alternator tested okay and the voltmeter in the cluster show good voltage. I plugged in and gets code stating there is a problem coming from the power relay, is this the pcm relay? Any thought would be appreciated, I hated paying someone several hundred bucks if it’s an easy fix I can handle. Thanks.

97% chance your alternator is bad. Often they test good on the auto parts store tester but are bad.

Replace it before you break down.

— Dave

Pick up something like this:Palumma Car Charger, 5V/3.6A Dual USB Port Safe Smart Quick Car Charger Adapter with LED/LCD Display Battery Low Voltage Warning Volt Meter Car Battery Monitor (Black)
Grab your multimeter and see what voltage you’re seeing at the batteries and at the back of the alternator. What till the GPR shuts off.