The battery energy storage system(BESS)is considered an effective method for wind power stabilization. The inconsistency of BESS is always ignored in current simulations with the whole BESS simplified as a battery cell. However

in practice

because of the large scale of batteries

the cell to cell variation is quite common in BESS. In the circumstances

the simplified model would cause overcharge or discharge

which significantly shortens the lifetime of batteries. This paper discusses the deterioration of battery pack and develops a detailed Thevenin model for BESS with distinct inconsistency. The presented model is suitable for power electronic design and offers useful information for control strategy. The proposed model is applied to fluctuation stabilization of wind power to show its advantage over the simplified model. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2014AA052003)and National Natural Science Foundation of China(No. 51307107

No. 51477098).