I've got spot lights fitted, use them every day and never had a problem.
to help the battery cope i turn them off a mile or so from my destination and let the bike tick over for a few mins before turning it off.
all so fitted LED side lights http://www.halfords.com/webapp/wcs/s...Id_165604#dtab and HID headlight.
these mods put less strain on the alternator and so far bike has been fine.