Power system for downhole toolstring

A downhole power system comprising:

• a first rechargeable energy storage device (ESD) within a toolstring to provide power to one or more tools within the toolstring;
• and
• a controller for controlling at least one of charging and discharging of the first ESD;
• wherein the first ESD is configured to be operable at a temperature range of −40 degrees C. to 250 degrees C. to:
• receive power from a power source at a first power level that is lower than a power requirement of a first tool in the toolstring, where the one or more tools in the toolstring comprises the first tool;
• and
• output power to the one or more tools within the toolstring at a second power level that is at or above the requirement of the first tool in the toolstring;
• and
• wherein the power system is coupled to a DC motor drive circuit, and a load of the DC motor drive circuit comprises a brushless DC motor;
• characterized in that the ESD comprises an ultracapacitor comprising an advanced electrolyte system (“AES”) and the AES comprises a salt of the following formula:
• wherein R1 is straight-chain or branched alkyl having 1 to 4 carbon atoms, R2 is methyl or ethyl, and X− is [B(CN)4]— or [BFn(CN)4-n]— where n=0, 1, 2 or 3;
• wherein the AES is purified to contain less than 1000 ppm of chloride ions, less than about 100 ppm of fluoride ions, and/or less than about 100 ppm of water;
• wherein the ultracapacitor comprises a positive electrode and a negative electrode, where at least one electrode comprises an energy storage media, the energy storage media comprising carbon nanotubes, the energy storage media consisting of at least 98% by mass elemental carbon;
• and
• wherein at least one of the electrodes has a moisture content of less than 350 ppm and chloride content of less than 300 ppm.