I have a temperature probe that operates using exclusively a 3.7V Li-ion battery. This is very inconvenient when the battery dies, and temperature data is no longer recorded until the battery is replaced. It would be much more convenient if this operated using a constant power supply that also had a 3.7V Li-ion battery as a backup for power outages. I'm uncertain of the current draw of the temperature probe but I believe it's less than 5A.
I know literally nothing about circuitry and I assume that this is not terribly difficult to do. If someone could point me in the direction of basic resources for designing a simple circuit, or help me along the process of what's needed to accomplish this.
Also as a note, these are primary 3.7V Li-ion batteries so there is no need to include recharging in the circuitry.
Any help would be greatly appreciated.