Battery pack including static memory and a timer for charge management

A computer system, comprising:

• a removable battery pack, comprising
• a rechargeable battery,
• a real time clock coupled to said battery for continually providing an indication of the present time,
• memory coupled to said battery for storing a timestamp of said present time indication and a numerator representing the remaining charge of said battery at approximately the time indicated by said timestamp, and
• battery pack communication means coupled to said battery, said real time clock and said memory for receiving, storing and transmitting said present time indication, said timestamp and said numerator;
• and
• a host computer for coupling to and receiving power from said battery pack, said host computer comprising:
• means for coupling to said battery pack for measuring the amount of charge provided to and provided by said battery,
• host computer communication means for coupling to said battery pack communication means for interfacing said host computer with said real time clock and said memory of said battery pack,
• means for detecting installation of said battery pack to said host computer, and
• processing means coupled to said host computer communication means, said detecting means and said measuring means, wherein said processing means retrieves said timestamp, said numerator and said present time indication after said detecting means detects installation of said battery pack, and thereafter, while said battery pack is connected to said host computer, said processing means periodically updates said numerator based on the amount of charge provided to and provided by said battery, and also periodically updates said timestamp with the current value of said present time indication.

A method for determining the elapsed time during which a battery in a removable battery pack of a computer system is self-discharging, wherein the battery pack includes memory, comprising the steps of:

• the battery pack continually providing a present time value;
• detecting whether the battery pack is installed on the computer system while the computer system is powered on;
• when the battery pack is first detected installed on the computer system, retrieving the present time value and a timestamp of the present time value previously stored in the memory of the battery pack;
• subtracting the retrieved stored timestamp from the present time value to calculate the elapsed time;
• and
• periodically reading a new timestamp of the present time value and storing the new timestamp in the battery pack memory while the battery pack is connected to the computer system and while the computer system is powered on.

A method for determining the amount of self-discharge of a battery in a removable battery pack of a computer system wherein the battery pack includes memory, comprising the steps of:

• the battery pack continually providing a present time value;
• detecting whether the battery pack is installed on the computer system while the computer system is powered on;
• monitoring the amount of charge added to the battery during charging and the amount of charge removed during discharging of the battery while the battery pack is detected installed on the computer system;
• retrieving the present time value and a previously stored timestamp of the present time value from the battery pack memory when the battery pack is first detected installed on the computer system;
• subtracting the retrieved stored timestamp from the present time value to calculate an elapsed time of self-discharge;
• calculating the amount of self-discharge by multiplying the elapsed time by a predetermined self-discharge rate;
• and
• periodically reading a new timestamp of the present time value and storing the new timestamp into the battery pack memory while the battery pack is detected installed.