I made a pretty cheap (30eu) 14.4v pack out of AAs. I run a 20w Bulb with that pack, that means the current should be below 2A (discharge).
Heres the problem, with out any load the pack measures 15-15.5v (18 right off the charger). Then i hook up a 20w halogen and it drops to 12-12.5v!! This pretty much is counter productive to overvolting!
If i hook up a 8w lamp i get 1v drop to around 14v, thats what i expected on the 20w.
What actual voltages are your 20w+ systems running?