CPU Upgrade on presario 12XL500

I upgraded the cpu from celeron 766 w/128 cashe 100 bus speed to 1Ghz pentium III coppermine pc 133. I also upgraded the HD from 6g to 20 g, 4200 rpm, IBM, & 320 m of ram. But now when I use the Nickel metel hydride battery that came with the laptop the screen flickers after bootup & then the unit powers down. I checked the power settings & turned all stndby & hybernation modes off. The battery display shows full charge. Question, does the 1ghz cpu use too much power resulting in power down? Operating sys. is win 2000 pro. compaq presario 12XL500. Cpu has speed step technology. BIOS is Phoenix 4.6. All softpaqs & win updates installed. Looking for advice & sugestions. Thank you very much.