mvs sarma, without regulation LED brightness won't be easily controllable, neither will the timing rate of the LED flashing if the internal oscillator is used, they're VCC sensitive so it would flash at different rates/brightness depending on the battery state. You might want to look at buck converters if you're going to use a 9V input, the gains in efficiency of using a switching regulator will be much higher than even a low current linear regulator. Give Lithium batteries a chance to as capacities are much better and you only need three cells for the same voltage an 8cell Nimh would use.