Dear flotulopex,

LDOs are a good choice as suggested by Luciano. Depending on your application if you are using a nanowatt PIC then your PIC may work within the range of 2V-5.5V or 2V-6.0 volts. If you are using CMOS logic as well then this should not be a problem. Also for alkaline batteries the cell voltage is 1.5V, but if you are using a rechargeable solution with Ni-Cd or Ni-Mh then your cell voltages are 1.2 volts per cell. So let us know more about your app.