I would simply leave the baettry alone until the night before your next game, then charge it up before you go to sleep or in the morning before you leave. That's the best way I know of to avoid messing up the baettry without a smart charger or discharger. Hope that's helpful!
well if you want a mostly metal elicrtec for a3150 then the M14 you were looking at seems like a great choice tbh. it will last you a long time if you look after it well, but airsoft guns arent designed to last too long.