Lightning shot clearly lowers energy cost to shoot arrows a lot more than it's supposed to (about 22% instead of stated 10%). Also quick shot alone seems to reduce energy cost a bit more than expected as seen from the following.
All of the following were gained with level 1-5 archers or rangers:
Level 1 in weapon skill, no talents: energy cost is 980 as expected.
Level 3 in weapon skill, no talents: energy cost is 943 as expected(*). (manual states 940)
Level 5 in weapon skill, no talents: energy cost is 900 as expected(*). (manual states 895)
Level 5 in weapon skill, quick shot: energy cost is 806, but 819 is expected!(**)
Level 1 in weapon skill, quick shot: energy cost is 884 as expected.
(*) Energy cost calculation for small reductions is a bit innaccurate. See
http://www.adom.de/forums/project.php?issueid=1435 and
http://www.adom.de/forums/project.php?issueid=1371 for more details.
(**) Level 5 weapon skill should reduce energy cost to 895, Quick shot should reduce it to 900, so formula should be 100000 / (100 + ((100000 / 895) - 100) + ((100000 / 900) - 100)) = 819 (with integer calculations)