sell the third pin to poster .....
Locally made UPS don't give a proper sine wave of output voltage as bridge rectifiers are used to convert dc of battery to ac and no conditioning circuits are used since they cost a lot). Capacitor driven items like fans, motors etc will give noise since the capacitor charge discharge wrt frequency of voltage and a square wave form disrupts this sequence resulting in heating up of windings and shortened life of tube lights etc (just putting the theory in simplest words) ... the laptop power sup including chargers having conditioning circuits to cater for variations in voltages.
In general it won't effect the supply or its charger or its battery .... again some laptops do not have a sofisticated supply and using these laptops on ups will reduce battery life cycle ...
a simple check is "SEE HOW MUCH TIME IT TAKES TO CHARGE YOUR LAPTOP BATTERY ON UPS AND THEN ON NORMAL POWER, IF THE BATTERY GETS CHARGED QUICKLY ON UPS THEN IT IS DEFINATELY REDUCING THE BATTERY LIFE"