Capacitor Filtering on a battery supply

[drigg]

I want to use a 12v NiCad battery pack to charger my mobile phone when I am in the bush for emergencies. I will be dropping the volts down with a 5 volt regulator.
My question is do I need to use a filtering electrolytic cap on the input and or output of the regulator?

 

[(*steve*)]

It would not hurt. However it would benefit you greatly to look at switchmode regulators. You will be able to get more than twice the energy from your battery into the mobile phone.