The battery life has only ever been an issue for me once, and that was before I got used to it. I rarely have four hour gaming sessions anymore, and when I'm home, I just drop it on the cradle. I keep the brightness at max, the WiFi on, and the system in standby, but you can change all those settings to extend the battery life. If I'm on a trip, I bring the charger with me. In the event that I ever play too long again, I'll just plug into the charger and keep playing. It's seriously no different than gaming on a smartphone or iPod. You just get used to it.
Finally, if you're going to cry that much about the battery life, Nyko does sell a higher-capacity battery for the 3DS.