2018 F150 XLT 5.0L coyote engine with 20.000 miles cranks slowly when hot. When I found out that the engine has 12 to 1 compression ratio I figured that the battery may have gotten weak (5yrs old from the shelf of the company) so I bought the best AGM 850 CCA battery I found on-line. It's a little better but occasionally still does the slow crank dance. Could the starter be drawing too much current and is this a fault of the stop/start function which I shut off. Any ideas?

 

i would start with checking and cleaning all the grounds

 

just had a simular issue with my 15 escape slow cranking turned out to be a bad ground wire from the battery to the body ground as per my bill from the local ford dealer. for d has a voltage sensor of some kind on the ground that went bad $70.00 just for the 15 inch long cable