Alt always helps. I am not 100% on it is a must though. I am holding steady 13.x voltage on full tilt with my stock alt (and my amps are seeing a .375 load). After a while of play it will eventually drop to 12.8 and chill, but I typically don't even keep it up that long. Basically if your respectful with your system (turn down at lights and neighborhoods) your alt should be able to recharge the batteries just fine.