This article from the technical experts at NICEIC looks at the types of batteries currently available, including their typical applications. However, the construction and chemical processes during the charging/discharging cycle of batteries is outside the scope of this article.
Once considered heavy and cumbersome and only capable of delivering a relatively small current in proportion to their size and weight, advances in battery technology have seen the performance of batteries improve significantly.
Batteries are the main power source for many electronic and wireless devices, such as mobile phones, smart home sensors, cordless power tools, etc. They are often employed, on a larger scale, within electrical installations to provide as a back-up source for many safety services (see Regulation 560.1 of BS 7671) and, more recently, in electrical energy storage systems (EESS).
A battery is an electrochemical energy source which can deliver only DC voltage and current.
Batteries are classified into two different categories:
(i) Primary cells – which are non-rechargeable
(ii) Secondary batteries – which can be recharged.
A primary cell is a battery that is specifically designed to be used only once and then discarded. The functionality of a secondary battery1 is exactly the same as that of a primary cell but is typically a group of one or more cells arranged in a series/parallel network so that the voltage or current respectively (or both) can be raised to desired levels. It is also capable of being recharged.
The zinc-carbon battery (Fig 1(i)) is one of the oldest types still in current use. Its terminal voltage2 is slighter higher than is available, size for size, for the alkaline (Fig 1(ii)) or lithium (Fig 1(iii)) battery. Its current output is the lowest of all the popular non-rechargeable battery types, which makes it suitable for small load applications such as torches.
The alkaline battery, when compared to the zinc-carbon, has a higher energy density3 and a longer shelf life. However, the lithium battery out-performs both alkaline and zinc-carbon batteries by a considerable margin. Its energy density is five times greater than an alkaline battery and ten times greater than a zinc-carbon battery.
Rechargeable batteries (secondary)
This category of battery can be recharged and hence re-used. Though the initial cost is typically more than for a comparable primary battery, when properly used and maintained they do have a significant life span, in terms of the number of times they can be discharged/recharged.
Great care must be taken to ensure that any replacement battery is suitable for use with the associated charging equipment. Attempting to re-charge a non-compatible battery may lead to non-functioning equipment or the risk from fire or explosion.
Examples of the common types of rechargeable batteries (Fig 2) include: lead-acid, nickel-cadmium (Ni-Cd), nickel-metal hydride (NiMH), lithium-ion (Li-ion), and rechargeable alkaline.
The lead-acid is the oldest battery technology still in common use. They are used mostly for larger power applications where weight is of little concern. They are typically used in central battery emergency lighting systems and for the back-up supply for fire alarm and detection systems, and in some uninterruptible power source (UPS) systems.
They can be used in home energy storage systems (EESS) as a cost-effective option. Where this may be the case, consideration must be given for the provision of adequate ventilation due to the risk from battery gassing during the charging process, manufacturer’s instructions should always be considered.
However, when compared with other types such as the Li-ion, they have a reduced lifespan and lower depth of discharge (their low energy density means they cannot be stored in a discharged condition).
Although these batteries are very rarely used today, they are relatively cheap and their discharge rate is very low when compared to Ni-MH batteries. One disadvantage is they have a ‘memory’. This means that the battery will remember the point in their charge cycle where recharging began.
Therefore, during subsequent uses, voltage will drop at that point as if it had been discharged. It is more viable to use a Ni-Cd battery continuously until it is totally depleted before recharging. When used in conjunction with manufacturer’s instructions, a nickel-cadmium battery can last for 1,000+ cycles before losing capacity.
These batteries are preferable to Ni-Cd batteries because of their lower environmental impact. This includes the materials used to construct the batteries and the safe disposal of spent batteries. They have a greater terminal voltage than for Ni-Cd batteries but less than for alkaline batteries.
The modern Ni-MH battery offers up to 40 percent higher energy density compared to Ni-Cd, powering devices for longer for an equivalent rated battery. However, it is less durable than the Ni-Cd and cycling under heavy load and storage at high temperature reduces its service life. The Ni-MH suffers from a considerably greater self-discharge when left unused than a Ni-Cd.
One of its main limitations is that the Ni-MH generates more heat while charging and requires a longer charge time than the Ni-Cd. The trickle charge is critical and must be carefully controlled.
Some advanced chargers provide a “step-differential charge” which allows for an initial fast charging state before reaching a threshold voltage; at which point the battery is required to cool before entering a state of trickle charge, where the charging current is continually reducing until the battery is fully charged.
There are many types of Lithium-ion batteries, and used in a wide range of applications. They are generally low maintenance and can resist the “memory effect” whilst tolerating a wider range of temperatures.
One disadvantage is their fragility, and the need for a protection circuit to keep them working safely, as required under the IEC 62133-2: 2017 standard when used in portable equipment.
Due to their ability for high energy release these batteries incorporate a fuse that operates on high current and temperature which may render the battery useless4.
Typically, where individual cells are arranged to form a battery, such as those used in electric vehicles, precautions must be taken to reduce thermal runaway between cells and prevent the risk of fire. Such precautions generally include thermal protection to limit the transfer of heat between cells, and fire blocking foam to suppress any fire.
This article has looked at the common types of batteries available, including non-rechargeable primary cells, and secondary batteries which can be re-charged. Also considered briefly was their operational characteristics and typical applications for use.
Where it is necessary to replace old rechargeable batteries, precautions must be taken to ensure the replacement battery and charging unit are compatible. In all cases when handling or using batteries for different applications manufacturer’s instructions should always be followed.
Footnotes & References
1 Often called storage batteries
2 Terminal voltage is the open-circuit voltage which is available before a load is connected
3 Energy density is the amount of energy stored per unit volume
4 Some types may incorporate a reset switch
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