Halogen 55/60 is what you want. In Europe the later 500/550 models were standard equipped with them. The only place I've heard about charging problems is in this forum...
But, if you fear charging problems, why not buy the Philips Ecovision? Philips did a smart job and it had excellent reviews too.
Specs from Philips:
# 20% less energy consumption (4 amps instead of 5 amps for H4)
# 10% more light than standard
# Twice the life expectancy of a standard lamp (that means 1000 hrs!)
# Reduction in your car's CO2 emissions by up to 36kg over bulb's lifetime.
# Quartz glass construction - safe to use with plastic lenses
# Standard wattage = fully road legal in the EU
basically these bulbs will pay for themselves during their lifetime.
If you want the ultimate, then there is the Philips X-treme Vision that promises 80% more light.