Went to put some dry gas in my bike and when I tried to start it it made a terrible grinding noise , like the starter was not engaging ,the battery was quite weak so I jump started it off the car , it started after having a better charge , but still ground a little , is this a low battery thing? 2008 fatboy, 13000 miles.

 

Probably is the battery, especially if it's the original one. Now get the battery load tested so you can be sure, not just suspicious. Also check both ends of both battery cables.
If you have to jump start it from the car, don't have the car running.

 

I installed a new battery back in February or Marchthat I bought from Oreillys and had to change it over the weekend. It was fully charged and still didn’t have enough power to turn the engine over fast enough to start. I bought a new Harley battery and it started right up. I tested the old battery and it tested good. I guess I’ll do it to the collection of old batteries.

 

Also had a bad experience buying one from O’Reillys. Only last two years.

 

Thanks for the battery feedback, I was more worried about the grinding noise , if that was a low battery thing , could it be the starter not engaging?

 

Could be poor contacts in the starter solenoid too. That would require removing the cap/cover and inspecting.