JD 240 series 2 will only start when boosted

[putland_22]

So my skid steer has 11.9 v on the battery and will turn over and over no problem but wont start and if i hook up my diesel truck to the battery it fires right up. the starter sounds fine and it used to start fine and then all of a sudden this problem started.

 

[skidsteer.ca]

Perhaps the battery voltage is to low to turn the fuel solinoid on until you conect the boaster cables. Your loader battery should have 12.4 to 12.5 volts even after sitting for a few days.
You indicate the cranking rpm seems fine, but if it is too slow that could cause a no start too.
Likely time for a new battery.
Ken