Apparently 20w (2 x 10w spots) pulls about 1.7 volts from a 12v battery when running, which is sod all.
I thought i'd give my battery a little booster charge last week seeing as the weather was getting very nippy, but when i first took it off the bike and tested the voltage straight away on my bench it was showing as 12.97v (which would be slowly dropping), and once connected to a charger it showed as fully charged in less than 30 seconds, so it was good to know that the electrical circuit and battery was all fine and was coping very well with the spots, headlights and heated grips on a high setting in very cold conditions.