Battery packs
What is a battery pack?
A battery pack is an interconnection of individual battery cells to adapt the voltage or capacity of the system to the individual application. For this purpose, the individual cells are connected in series to adjust the voltage or/and connected in parallel to adjust the capacity of the battery pack. To protect the battery pack, the pack is protected either by housing, a heat shrink tube or by a sheath. In a battery pack, the connection between the consumer and the battery pack is usually made by a connector, a cable, a terminal port, screw connectors, possibly induction and many more.
A battery pack can consist of different cell technologies, but the cells must be of the same type from one manufacturer. The cells must be identical in terms of cell size, cell technology, performance values - i.e. voltage and capacity - and load capacity. They should also come from the same batch.
How is a battery pack constructed?
A battery pack can be constructed in a wide range of ways, from a complex structure to a simple design. All battery packs consist of several cells, connectors, cell holders and a connection such as a cable or aplug. Depending on the battery pack, the construction is protected by a casing or heat shrink tubing. In contrast to NiMH and NiCd battery packs, lithium battery packs have a protective circuit and are also equipped with sensors and communication options, and possibly also a battery management system.
The individual structure of a battery pack is shown in the following diagrams.
What are the advantages of a battery pack?
The following are the advantages of a battery pack:
- customisable
- safer than using single cells (housing)
- voltage and capacity can be customised
- housing and form factors are customisable: holders can be incorporated into the design
- interchangeable system
- better handling
- realisable as a customised system solution: performance and energy consumption are optimised (holder, charger, device control).
Following on from the advantages just mentioned, here is a table for a specific overview of the advantages of battery packs.
What is the difference between a rechargeable battery and a battery pack?
A battery pack is an interconnection of individual battery cells to adjust the voltage or capacity of the system to the individual application. A battery pack thus consists of several secondary cells connected together.
An accumulator, also known as a battery or secondary cell, is a rechargeable galvanic system consisting of two electrodes, the cathode and anode, and an electrolyte that electrochemically stores electrical energy.
A battery consisting of one or more interconnected primary cells is not rechargeable, unlike a battery pack.
What types of battery pack are there?
As a rule, a distinction is made between four different battery types: Nickel-cadmium (NiCd), nickel-metal hydride (NiMH), lithium-ion (Li-ion) and lithium-polymer batteries (LiPo, LiPol). Of course, there are also lead-gel and lead-acid batteries, you can find more details here.
Nickel-cadmium batteries: NiCd batteries are particularly suitable for drills and circular saws, are relatively insensitive to cold and have a long life of over 1500 charging cycles. NiCd batteries have a lower capacity than other types of batteries, have a memory effect, which means they must always be completely discharged before recharging, and are very harmful to the environment because of the cadmium.
Nickel-metal hydride batteries: A NiMH battery has about 50 % more capacity than a NiCd battery of the same size. The NiMH battery should also be fully discharged before recharging, otherwise, the battery inertia effect occurs, which reduces the capacity. With 500 to 1000 charging cycles, the NiMH battery is somewhat shorter-lived.
Lithium-ion batteries: Li-ion batteries are smaller and lighter than NiMH batteries with the same capacity and are on the same level with 500 to 1000 charging cycles. Li-Ion batteries have no memory or inertia effect, and self-discharge is also very low.
Lithium-polymer batteries: LiPo batteries can have any shape and are therefore very suitable for devices with little space. The self-discharge is also very low here and there is no memory/battery inertia effect. The life expectancy of 300 to 600 charging cycles is much lower than that of other rechargeable batteries.
Lithium-iron phosphate batteries: LiFePo4 batteries are another version of lithium-ion battery packs with a cell voltage between 3.2 and 3.3 V. The positive electrode is made of lithium instead of lithium. The positive electrode consists of lithium iron phosphate instead of lithium cobalt, while the negative electrode contains lithium embedded in graphite. The life expectancy here can be up to 4000 - 5000 charging cycles.
What does Ah mean by battery packs?
The abbreviation "Ah" stands for ampere-hour. An ampere-hour is a unit of measurement for the electrical charge of a battery. One ampere-hour is equal to the charge that flows through the arresters in one hour at the constant current output. The unit Ah is often used to indicate the capacity of accumulators.
However, this should be clearly distinguished from the actual capacity. This is given in watts. Multiplying the voltage (volts) by the nominal capacity (Ah) of a rechargeable battery gives the actual energy storage capacity in watt-hours (Wh).
What does Wh mean by a battery pack?
Watt-hours (Wh) indicate the amount of electricity that can be stored in a battery pack. The product of capacity (Ah) and voltage in volts (V) gives the watt-hours.
A distinction is made between usable energy content and rated power. The nominal power is defined by the nominal voltage and the nominal capacity. This value is the starting value for the evaluation of a battery pack and is derived from the manufacturer's specifications. The usable energy of the battery pack, however, can deviate greatly from this value due to environmental influences such as temperature and ageing.
How long does a battery pack last?
How long a battery pack lasts, or rather how long its service life is, depends on the number of charging and discharging cycles as well as on its calendar age. When experts talk about service life, they usually mean a remaining capacity of 80 %, based on the number of cycles specified by the manufacturer. However, there are also deviating values, e.g. 60 - 70 %. A charge cycle describes the time the battery needs to be fully charged. The discharge cycle thus corresponds to the time the battery needs to be discharged. The life of a battery is measured in months or years as well as in charge and discharge cycles, as this includes the factor of frequency of use and the ageing factor.
What factors can affect battery life?
The life of a battery can be affected by many factors. The main cause of performance degradation and accelerated ageing of a battery system is the accelerated ageing of chemical components. Essential factors for this are:
- Large temperature fluctuations (too hot, too cold)
- Overcharging or deep discharging
- Frequency of use
- Short circuit
- Storage errors (storage in discharged condition, or storage in full condition depending on the technology).
All of these factors can harm the battery's lifespan. Nevertheless, the service life can be influenced enormously through correct use.
How can you extend the life of a battery?
It is normal for a battery to lose power over time, but there are ways to significantly extend the life of a battery. It is important not to keep the battery permanently fully charged on the mains. Experts recommend recharging an iPhone battery between 40 and 85%. Try to avoid large temperature fluctuations (too hot, too cold); a temperature between 15 and 25 °C is usually recommended. Charging the battery should be done between 5 and 40 °C.
What is the best way to store a battery?
Below we have prepared a checklist for you on how best to store batteries to protect them from weathering:
- Remove the battery from the device and clean it of dirt and grime
- Store your battery in a cardboard box to protect it from moisture, cold and sun
- Dry basement rooms or a garage are particularly suitable storage locations for rechargeable batteries, as storage temperatures between -10 and +35 °C are recommended for rechargeable batteries
- Store your battery in a safe place out of reach of children
- Store your charger separately from the battery
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