a car charger can ruin a battery in the long run you need a bike battery charger put it on charge day before using it and as soon as its charged a bike charger automatitly goes onto trickle charge to keep it fully charged then after beeing out leave the lamp on to fully disgarge and then back to the begining if you dont let the battery fully discharge then fully charge on a regular basis parts of the battery go stail so they no longer work as well so you could be carrying a big 18ah battery around but only getting the same light time as you would out of a little 6ah battery look after a batter