I second cleaning the terminals, I was having similar symptoms on my ZJ and all it ended up being was corrosion on the battery terminals and battery cables.
2005 TJ Rubicon - 6" Rough Country Long Arm Lift, 35x12.50 Falcon Wild Peak A/T, Body Armor Rockcrawler Side Guards, MOPAR Rock Crawler Winch Bumper, ENGO E9000 Winch, Body Armor Boly in Cage - Mine
1998 Grand Cherokee - Daily Driver/tow rig - 2" BB, 31x10.50 A/T's - nothing special
2012 Grand Cherokee - Wife's ride
2010 JK Unlimited - stock - Wife's Ride! - SOLD
1997 Grand Cherokee Orvis V8 ------ 2.25" BB - SOLD!