esv stands for expanded scale voltmeter.Its a meter that checks the batteries in the radio and plane under load,gives you as idea as how much if any flying time is left on the batteries,I think a quick charger for the field is a must.Many times I've ran the batteries down or someone forgot to turn off the plane,which would end the day,15 to 25 minutes on the quick charge and full of juice for the wild blue younder.By all means,do some researching and start a second plane for the learning curve,good flying weather is around the corner then you need to be at the field not building.