How to connect the lithium battery is reasonable

Portable devices that require high power are generally powered by a battery pack in which two or more batteries are connected in series. If a high-voltage battery is used, the size of the conductor and switch can be made small. Medium-priced industrial power tools generally use batteries with a voltage of 12V to 19.2V; advanced power tools use batteries with a voltage of 24V to 36V to obtain greater power. The automotive industry eventually increased the ignition battery voltage of the starter from 12V (14V in fact) to 36V, or even 42V. These battery packs consist of 18 lead-acid batteries connected in series. In the early hybrid cars, the battery pack used to supply power had a voltage of 148V. The battery packs used in newer models have voltages as high as 450V to 500V, and most of them are nickel-based chemical batteries. A nickel metal hydrogen battery pack with a voltage of 480V is composed of 400 nickel metal hydrogen batteries connected in series. Some hybrid cars have also been tested with lead-acid batteries.

42 V car batteries are expensive, and, compared to 12V batteries, it generates more arcs on the switch. Another problem brought by the use of high-voltage battery packs is that one of the batteries in the battery pack may fail. This is like a chain, the more batteries connected in series, the higher the chance of this happening. As long as there is a problem with a battery, its voltage will drop. In the end, a “disconnected” battery may interrupt the flow of current. It is not easy to replace a “bad” battery, because the old and new batteries do not match each other. Generally speaking, the capacity of new batteries is much higher than that of old batteries.

Let’s look at an example of a battery pack. The third battery only generates 0.6V instead of the normal 1.2V. As the working voltage drops, it reaches the critical point of the end of discharge faster than a normal battery pack, and at the same time, its use time is also drastically shortened. Once the device cuts off the power supply due to low voltage, the remaining three batteries that are still intact will not be able to send out the stored power. At this time, the third battery still exhibits a large internal resistance. If there is a load at this time, it will cause the output voltage of the entire battery chain to drop significantly. In a set of serial batteries, a battery with poor performance is like a plug blocking a water pipe, which will produce huge resistance and prevent current from flowing through. The third battery will also be short-circuited, which will reduce the terminal voltage to 3.6V, or disconnect the battery pack link and cut off the current. The performance of a battery pack depends on the performance of the worst battery in the battery pack.