A hygrometer or hydrograph is a tool used to measure the degree of humidity, or other gas. The electric hygrometer consists of two electrodes spiral-wound. If applied to these electrodes an alternating voltage, the tissue is heated and part of the water content evaporates. At a defined temperature, a balance between evaporation by heating the tissue and absorption set aguto ambient moisture lithium chloride, a highly hygroscopic material. From these data sets accurately the moisture.

Within the wide range of batteries on the market we can differentiate two large groups, disposable batteries and rechargeable batteries.
Disposable batteries are those that only allow a single use and when they are exhausted they can not be recharged. These batteries can store their energy for years.

Rechargeable batteries are those that can be recharged once exhausted. This type is losing charge when they are storedaccording to voltage. The most common we can find them of 1.2V and 3.7V

As a last point you have to take into account that lithium batteries, Lipo, Life etc. Due to its composition, specific loaders should be used.