I've been impressed with L&M solo and commuter models. I was at Sears last week and a night time commuter was using the solo and it was fairly impressive. Before I liked the commuter for the side visibility slot.

I ran across some light yesterday that allowed you to separate the light and the battery pack so you could mix light and different types of batteries, Lead Acid, NiMh, etc. Don't know about connectors. Check out light reviews at www.mtb.com, if you haven't already. They have an interesting light shot out demo.