Methods and apparatus are provided for continuously powering tools downhole for extended periods of time, such as for the life of the producing well. Batteries may power the downhole tools, but traditionally, the batteries may last up to 2 years, and in some cases, up to 5 years may be reached with an optimized data sampling rate and power management scheme. After that time, operations may be halted temporarily for replacing the batteries. According to embodiments of the present invention, in contrast, rechargeable batteries may be utilized downhole to provide power to operate the tools, and rather than halting operations and retrieving the rechargeable batteries to the surface for recharging, reserve batteries may be used for recharging the rechargeable batteries. In many cases, these well tools may be designed to operate for a long period of time (e.g., around 10-20 years), depending on the life of the producing well.