18650 battery voltage is a vital parameter of 18650 lithium battery. To master basic knowledge of 18650 battery voltage plays an important role of scientifically charging& discharging and protecting 18650 battery. This article tries to establish 18650 battery voltage system through explaining following parameters:
1. work voltage, also called rated voltage of 18650 battery. This voltage is 3.7V, which equals voltage of Ni-Cd or Ni-MH battery in three-series configuration. Some domestic lithium battery manufacturers might design 3.6V work voltage.
2. Limit charge voltage: maximum limit to 18650 battery voltage, which is 4.2V. 18650 battery charge is a process with voltage rising from 3.7V to 4.2V. After completion of this process, continuous discharge could cause battery overcharge.
3. Discharge cutoff voltage: that is, the minimum work voltage under which continuous discharge is unsuitable. This cutoff voltage is 2.75V. if battery discharge below cutoff voltage, over discharge occurs, which could destroy 18650 battery electrode structure, cause irreversible reaction of li ions and affect 18650 battery lifetime.
Due to severe damage of overcharge and over discharge to 18650 battery, electric circuit protection is equipped on 18650 battery to automatically stop charge& discharge when upper and lower voltage limits reach.
Batterypacks could be assembled with 18650 battery in series, parallel and series& parallel ways.
1. 18650 battery pack in parallel form: capacity equals sum of battery cell capacity; voltage is same with rated voltage of single voltage. For instance, for 18650 battery pack assembled with two 2000mAh cells in parallel, voltage is 3.7V and capacity 4400mAh.
2. 18650 battery pack in series combination: capacity remains unchanged; voltage is sum of 18650 battery cell voltage. Take 18650 battery pack in three-series form for example, voltage is 11.1V whereas capacity remains 2200mAh.
3. 18650 battery pack in series& parallel way: for example, for 18650 lithium battery pack in three-series and two-parallel combination, voltage is 11.1V and capacity is 4400mAh.
The above 11.1V is also work voltage of 18650 after series& parallel combination. Besides, charge limit voltage and discharge cutoff voltage varies as per series number. For instance, charge limit voltage of three-series& two-parallel battery pack is 12.6V whereas cutoff voltage is 8.25V.
Therefore, different battery combination ways have generated diverse 18650 capacity. Owing to different capacity and voltage, 18650 batteries are used in more fields.