in Nigeria the Electric is not stable ( at times higher or lower than the standard 240Volt ). Do i need to use a UPS (battery backup) together with a voltage regulator? .
How much unstable? Asking without perspective (ie numbers) means everything or nothing can be recommended.
For example, normal voltage for any computer is even when incandescent bulbs dim to 40% intensity? How often is your voltage dropping that low?
Voltage regulation is what every supply for all electronics must do. For example, normal voltage for a laptop is anywhere from 85 volts to 265 volts. Demonstrating but again why numbers (perspective) must always be included in any technical recommendation.