The problem with non-rechargeable batteries is nobody is developing better lights for AA or AAA batteries anymore. Not worth the hassle or weight and bulk.

The only good replaceable battery bike headlights I've seen are the Serfas SL-255 (discontinued but still available) and the Busch & Muller Ixon IQ Premium.

The Serfas SL-255 takes 2 AA batteries, isn't too heavy and bulky, has high and low steady and bright flashing modes. Maximum brightness is 255 lumens, as the model implies. But it's a spotlight beam, very narrow. With alkaline batteries it gradually dims so after a few hours the bright setting is barely visible. With NiMH rechargeables it stays brighter through most of the runtime but extinguishes suddenly. I use it only as a backup, sometimes as a loaner on casual group rides because invariably some ninja shows up for nighttime rides without lights.

The B&M lights are very good and adequately bright. But no flashing mode (it's prohibited in Germany where B&M are made, and they don't make a special model for the US). But with a payload of 4 AA batteries, even with lighter weight NiMH it would still be bulky and heavy for a helmet.

If you want to rig up a separate head and tail light system, check out the Cygolite Hotshot taillights, the lightest weight and brightest bang for the buck taillights. They are so piercingly bright when viewed from directly behind it helps nudge tailgating drivers to the side.The light aperture is very narrow, so it's not as visible from the sides. But it's a very effective day/night taillight.

We don't really need 500 lumens for a to-be-seen helmet light. I use small, lightweight USB rechargeable helmet lights that get attention just fine from drivers. Check out the Blackburn 2'Fer, and 2'Fer XL. The best buys are in pairs and often a little cheaper via Amazon. I've used a 2'Fer for going on 4 years now, no problems. Good light. Each unit has four modes: steady white and red, flashing white and red. Just push the button to reach the appropriate mode for head or tail mounting.

The Light & Motion VIS 360 may be the best dedicated, integrated helmet mounted head/tail light system for the money.