the longer the cord,the more drop.it's mainly amp draw that is the concern.it will overheat if too much is pulled through it,and can damage equipment.with a charger,you shouldn't be pulling that much.use the shortest cord you can.14 gauge should work under 25 feet,and probably to 50,but i would go with 12 gauge.it never hurts to go heavier.it's worth it for the added insurance.and it's cheaper than a charger
i have a different charger problem the charger i have is about 5 years old and it dosent charge the battery fully never has i have the red black and green bubble window on the battery it only will charge it to black which is 50% or so it has an automatic deep cycle switch on it which is the cycle i use it has 12 and 24 volt i use 12 in the past 5 years i have gone through 3 batterys i dont know what i am doing wrong after an hr or few the needle bottoms out at 0 and starts to jump to 8 then back to 0 and over and over if the charger is shot that will suck i gave 75 bucks for it and expected a life time of use please help.....jim
Don't rely on those colored ball indicators. Use a volt meter and check the voltage after your black ball appears. Your charger (if working properly) will switch between full and low when the battery is fully charged. The only way to determine if the charger is doing the job is with the volt meter.