I bought a charger from batteryspace.com after I fried mine. $23 + shipping, worked out to $30. Works great!
IF I WERE you, I would consider getting a bigger battery to get the full capacity that you're after. OR get a second battery AND charger from batteryspace.com.
Did you get a new light system recently? Niterider Rage HID? It's rated for four hours burn time - do you have a very long commute?
For me, charging my lights is easy. I just hook up the charger when I park the bike at home each day. If I were dealing with two batteries or two chargers, the hassle of the battery shuffle would drive me bonkers.