I have a 2018 GMC Crew Cab 4X4 Sierra SLT with e-assist and 20,000 miles. Hoping I might find some answers or advice as to what I perceive as a problem here. Last summer when temperatures reached 115 degrees, I parked my truck to pick the grand kids up from school. Went back to the truck the battery was dead and needed a jump. On the way home the voltmeter was showing just over 9. I had the battery and alternator checked and both were good ( battery wasn't 5 years old). Low voltage output was normal during over 110 degrees days. I learned about the EPM and the ability to use the e-assist to jump start. I didn't experience the need for a jump and haven't tried the e-assist to start. Everything has worked well since no weather over 110 degrees. Last night making a 100 mile drive to the speedway races, temperatures reached 112 degrees and my voltmeter dropped to 11 or 12. I understand that with the EPM system, volts are adjusted in order to maintain battery efficiency and life, hence the change in volts is normal. Although I don't usually see that much variance in my voltmeter, it my fluctuate between 13-14 and very seldom if ever over 14. I'm wondering what causes the drop in the extreme weather. If the battery is bad, will the e-assist still jump. From the instructions, it sounds like the e-assist battery may not be able to charge the main battery. " When the jump start is complete, the display will show “JUMP START COMPLETE, ATTEMPT START or JUMP START DISABLED”. Also, " jump starting may be unavailable due to the 12-volt battery charge level " I don't like the idea of being stuck in weather over 100 degrees anywhere, does anyone have this experience or any insight as to what's happening, and what I can do to restore my confidence in my truck not leaving me stranded?