low power constant voltage source

i have a circuit which is driven by 3 V battery source. The circuit consumes very less power.
The circuit needs 2.5 v constant supply all the times and even if the battery voltage dropped due to battery aging.

- could somebody help me with a simple circuit please.

thanks in advance

yagtoby

If the battery voltage does not drop below 2.55 volts, then just use one of these:LP2980IM5-2.5 or any equivalent Low Dropout Linear Regulator. The data sheet for the part shows how to hook it up:
https://www.electro-tech-online.com/custompdfs/2006/06/LP2980.pdf

If the battery voltage goes from 3.0 and down to below 2.5 Volts, then it will get too complicated and you might want to consider using a different battery type. For example a Lithium-Ion battery should operate from 3.2 to 4.2 volts.