You'll eat your battery in a hurry (if it's a lead acid battery) with routine depth of discharge much over 50%.
You can get thousands of charge/discharge cycles from a lead acid battery if you limit discharge to 10%. You'll get a couple of hundred cycles, maybe, if you limit discharge to 50%. But suck 12AH out of your 12AH battery (which is 100%) and you'll be lucky to get more than three recharges before it gives up.
Incandescent lighting is really a backwards approach for a bike anymore. You can get more light of a better color with less than 10W of high flux LED. Halogen bulbs make about 15 lumens per watt-- a little more for high power bulbs, and a little less for low power ones. So you'll be doing well to get 750 lumens from 2x25W halogen lamps.
For contrast, have a look at
this high flux LED bike light. The battery pack has a rating of under 32 watt-hours, and the claimed runtime is three hours at full blast. So it's making 900 lumens from around 10W, and as a result it gets to be small and convenient to mount, with a small battery pack.
LED is really the only lighting technology that makes sense for bicycles anymore.
Chalo
