One of the major issues I had using headlights that were rechargeable is that I would forget to plug the thing in when I came in from a ride, then wouldn't be able to ride the following day. If you used rechargeables for multiple rides, you'd potentially have similar issues, either you recharge every ride, or you find yourself waiting until they dim and then it's too late.
I've used several different blinkies, the Planet Bike Superflash being about as good as any. I'd say, forget the 200 hours, replace the batteries whether it needs it or not. You don't want to be laying in a casket while some guy says, "Well, he's dead, but at least he saved $1.25!"
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"be careful this rando stuff is addictive and dan's the 'pusher'."