A portable device that requires a high amount of power is generally powered by a battery pack in which two or more cells are connected in series. If a high voltage battery is used, the size of the conductors and switches can be made small. Mid-priced industrial power tools typically use batteries powered from 12V to 19.2V, while advanced power tools use batteries from 24V to 36V for greater power. The automotive industry eventually increased the ignition cell voltage of the starter from 12V (actually 14V) to 36V, or even 42V. These battery packs are made up of 18 lead-acid batteries in series. In the early hybrid cars, the battery pack used to supply power had a voltage of 148V. The battery packs used in the newer models have voltages ranging from 450V to 500V, mostly nickel-based chemical batteries. A nickel-metal hydride battery pack with a voltage of 480V is made up of 400 nickel-metal hydride batteries connected in series. Some hybrid cars have also been tested with lead acid batteries.
The 42 V car battery is expensive, and it produces more arc on the switch than the 12V battery. Another problem with the use of high-voltage battery packs is the possibility of failure of a certain battery in the battery pack. It's like a chain, the more batteries are connected in series, the higher the chance of this happening. As long as there is a problem with one of the batteries, its voltage will decrease. At the end of the day, a “disconnected” battery may interrupt the delivery of current. It is not easy to replace the "bad" battery, because the old and new batteries do not match each other. In general, the capacity of new batteries is much higher than that of older batteries.
Let's look at an example of a battery pack. The third battery produces only 0.6V instead of the normal 1.2V (Figure 1). As the operating voltage drops, it reaches the critical point of discharge end faster than the normal battery pack, and its use time is also sharply shortened. Once the device is powered off due to low voltage, the remaining three sections of the battery will not be able to send the stored power. At this time, the third battery also exhibits a large internal resistance. If the load is also present at this time, the output voltage of the entire battery chain will be greatly reduced. In a set of serial batteries, a poorly performing battery, like a plug that blocks a water pipe, creates a huge amount of resistance that prevents current from flowing. The third cell will also be shorted, 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.
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