The lithium battery of this product can be charged notonly by solar energy, but also by auto battery and household battery. Then the lithium battery supply power for the cooling bag, to keep the temperature inside between 13 - 18 degree Celsius, which will keep food and vegitable fresh, also will prolong time of fresh. The body material is nylon, all waterproof, can endure dirty. It is indeed a necessary for household, business trip and car owners. Functions: 1, it can work under sunshine while cooling. 2, without sunshine, it can cooling powered by auto battery or AC electricity. 3, without any power, it can cooling via accumulation. Deacription: 1, solar power: 4W/2W 2, standby battery: when the power is cut off, it can prolong fresh time for 4 hours by the high capacity lithium battery. 3, nylon material,full waterproof, high airproof, endure dirty. inside material is high-performance heat preservation PVC heat insulation cotton 4，refrigerating capacity：0.01P, no need for ice crystal,just turn the switch then the tempreture will be lowered to 15 degree Celsius in about 20 mins ( tempreture of environment is about 32 degree). 5，energy-efficient, environmental, can be reused, low power consumption 6,it can be used for keeping fresh for vegitable, fruit, fish, red wine, coca cola, and so on. 7, this product is different from prevenient cooler bag or AUTO cooler bag, it is low power consumption,quickly lowering tempreture, long time of keeping tempreture. It will never happen that the accumulator eats electricity fast while powered by auto. 8, if charged by AC electricity, it will only cost 1 kilowatt hour.