A battery is a box of electricity. 电池是一盒电。

　　It stores chemical energy and this chemical energy changes into electricity. 它能储存可以转化为电能的化学能。

　　Can you name the things that need batteries? 你能列举出需要电池的物品吗？

　　A clock may need a battery. 钟表可能会用到电池。

　　A car needs a battery to start its engine. 汽车需要电池来发动引擎。

　　Many things around us are useless without batteries. 我们身边的很多东西没有电池就一无是处。

　　Do you know that batteries were very huge a long time ago? 你知道很久以前电池的体积很大吗？

　　People couldn't carry batteries because they were too heavy. 人们携带不了电池，因为它们太笨重了。

　　So, scientists developed small batteries. 因此，科学家研制出了小型电池。

　　Now, we can carry them everywhere. 如今，我们去哪里都能带上它们。