Rocket wont start ???

Good plan..I have a little device/tester that shows the draw down voltage when starting. It uses LEDs and the lowest voltage LED stays lit to show the voltage. It shouldn't go below 9 volts when cranking according to my tester. If it does, things are questionable.
 
Hi, new to the group.
I have had two rocket 3 BT’s, both had battery issues.
I had to call the RAC after not starting but lighting up the dash, after refuelling.
RAC took off the terminals, cleaned them, applied copper grease and never had an issue again.
Maybe I was lucky.
Hope this helps
Dave