1 SEC = 12 e.u.
SB capacity = 1800 e.u.
You can recharge SB whenever you want, no matter if isnt empty
Max sneak by skill points its 200.
And from the wiki:
With the item perks Ghost and Ghost II (unlocked with skill 150 and 175), you will get a +20 skill bonus if you are within 1 and 5 hexes from a wall, respectively. Furthermore, if the path between the sneaker and the observer is obscured by a scenery that blocks movement but not sight, the sneaker gets +10 to his skill.
So i think max is 200+25(lj)+20(ghostI)+20(ghostII)+10(object)= 275. (but im not sure if both ghost stack, so max can be 255)
Of course you need to be next to a wall AND bloqued by an object. The most comon bonus will be lj+ghostII, so 245.