Why does the newly purchased laptop battery become about 5% in less than a few days?

It is not a battery problem, it should be a usage problem.
The most feared problem of batteries is heat. Because heating batteries will wear out rapidly.

When using a laptop, it is best to remove the battery and plug in the power source to ensure battery life. If you use the battery to play directly, you must not play large-scale games. The power consumption is too high, the battery will heat up quickly, and the loss rate will increase. Also, when playing, be sure not to put it in a soft place such as a bed, so that the heat vent is blocked and the battery will generate a lot of heat.
In addition, the battery loss rate is not fixed. For example, the next time you charge to play after your battery runs out, the loss rate may become 3%-4%.