An M20 pilot suffered a complete electrical failure due to a dead battery.

Narrative

Complete electrical failure on battery one during climb out with rapid loss of lights; radio and avionics; within a few minutes of departure. I had reached for pitot heat switch and inadvertently hit the vacuum pump standby switch which appeared to trigger the electrical failure with rapid battery power loss. Resetting the switch was to no avail. Annunciator worked to identify rapidly declining battery power. Plane had been flown less than 2.5 hours from annual; battery checks reportedly had been normal. I attempted to contact Departure on frequency given by Tower after my VFR departure. After an initial attempt to contact Departure; I switched back to Tower to inform them of my situation. Tower indicated radio was difficult to copy. I declared an emergency and switched to my hand held transceiver. I had no lights and viewed the panel with a flashlight held in my mouth. I lowered landing gear by hand and requested a low pass fly by to ensure gear was down. Tower requested a second low pass; which was accomplished. I was assured gear were down; and made a 90Kt; no flap approach to a smooth; uneventful landing. Maintenance later stated half the plates of battery 1 were exposed and it did not have sufficient fluid to be tested by a hygrometer. Tower was very helpful in this emergency.