Electrical power storage for downhole tools

A tool for use in a subterranean well, the tool comprising:

• an electrical power source which stores electrical power;
• an electrical load;
• control circuitry which controls activation of the electrical load;
• a switch which selectively permits electrical current flow between the electrical power source and the control circuitry;
• and
• an electrical generator,
• wherein the switch permits the electrical current flow between the electrical power source and the control circuitry in response to generation of electrical power by the electrical generator.

A method of activating a downhole tool in a subterranean well, the method comprising:

• displacing at least one of a fluid and an object at the downhole tool in the well;
• generating electricity downhole in response to the displacing;
• permitting electrical current flow between a downhole electrical power source and a downhole control circuitry in response to the generating;
• and
• after the permitting and in response to detection of a predetermined signal, the control circuitry causing activation of a downhole electrical load.