Fenix UC30 or UC35

I can't decide between the two models. The light output levels are similar.
I have a few questions. What's the highest capacity battery the UC30 can use?
Which would you choose and why?
How long does a charged 18650 hold its charge?
What order are the light modes for the UC30?

output is indeed the same. UC30 should be able to take any 18650 you want to put in it. I prefer the UC35 because of the extra unch where the mini USB port is. Look closely at that inch right behind the reflector on the UC35 notice the low wide cooling fins around that part of the body. UC35 has superior heat sinking than any other light in the class because of this. Have big fat 3600mah Orbtronic 18650's shoved into each light no problem. Both lights go turbo-eco-low-medium-high press and hold for strobe.

Celtic both lights have the same UI?

Yes both lights have the same UI unless I totally missed something when I read the manuals. It is the same UI as the PD35. Out of the box when you install a fresh cell and turn the light on for the first time it comes on in turbo or is supposed to from the factory. Reading the manuals the order does indeed start on turbo then drops to eco then low then med then high press and hold for strobe.

oops sorry OP I just double checked UC30 does NOT have eco so its 4 modes plus strobe not 5. UC30 mini USB port is also not waterproof like it is on UC35.