What would be the most likely cause for my lxph05 brushless LXT hammer drill to intermittently not turn?

probably the motor controller, brushless motors have a little computer that tells the motor when to activate each electromagnetic winding. The motors themselves are just bearings, windings, and magnets so they are fairly tough.

I also have the same dilemma,and of course,it occured 1MONTH after 1year warranty expired.I know my batts r still fine,as I recharge em on my foremans kit.
My charger plays a tune,then just blinks red,green....etc.Wish I had some tips to try,from an electronics brain-type person.......lol,good luck::

I answered that question already on another post, but if you need to know how to remove the chuck I have detailed instructions in the TIP SECTION on how to do this. Let me know if you need more help

Battery is shot. Replacements are $75 - $100. If its new you have a 1 yr warranty.

This is more then likely caused by the plastic gears inside the drill wearing down. Makita may replace/repair under warranty depending on when you purchased the drill.

JUST NEEDS A NEW SWITCH, EASY TO CHANGE WITH A LITTLE PATIENCE. YOUR LOCAL SERVICE CENTER CAN SELL YOU ONE OR WALK YOU THROUGH IT!! THE OTHER THING IT COULD BE IS THAT THERE IS A CHUNK OF DEBRIS IN THE TOOL OR THE HOUSING IS JACKED UP WERE IT HOLDS THE SWITCH INTO PLACE! I HAVE SEEN ALL SORTS OF THINGS HOLDING UP SWITCHES IN CORDLESS TOOLS!!!!! WORSE CASE IT WILL COST YOU AROUND $50 FOR A NEW SWITCH POSSIBLY ALLOT LESS. THANKS JIMS TOOL SERVICE

i have both the hammer drill and impact driver and have been interchanging the batterys without any problems

You say will not stay charged? Over what time period? Are you aware Nicad and NiMh rechargeables discharge naturally at 1% per day so where does that leave your power tool after 3 months? Furthermore they only have around 1000 charges in their useful life so you can immediately see how these tools are not for intermittent(ie handyman) use.

looks to me like a defective batterie

i'm afraid u have to replace your armatures..