⑴ Be beautiful to look at, trademark (design mark and brand tube);
⑵ Voltage limitation: combine batteries in series to get high voltage;
⑶ Protect battery: prevent battery from short-circuit and extend the cycle life;
⑷ Size limitation;
⑸ Ease to transportation( design of paper cabinet and paper box);
⑹ Especial function design, such as waterproof, especial surface design.