Lead acid batteries are cheap, convenient and they work for many battery power applications. They are probably best known for their use in vehicles where they supply the power for everything from starting, to the electronics and much more.
The lead acid battery has many advantages for automotive and many other uses: they have a large current and surge capability, which is ideal when being used to start internal combustion engines.
As a technology, lead acid batteries are well a well established technology and they can be easily manufactured with relatively low technology equipment.
Lead acid battery basics: how do they work
When looking at how a lead acid battery works, it is necessary to look at the basic components. The battery has comparatively few components - essentially there are four main elements:
- Positive plate: This is covered with a paste of lead dioxide.
- Negative plate: This is made of sponge lead.
- Separator: This is an insulating material between the two plates, but it allows the electrolyte and the ions into it to enable conduction without the two plates touching.
- Electrolyte: This consists of water and sulphuric acid
These constituents are all contained within a plastic container which acts to keep the electrolyte in and the battery together.
The overall battery will normally consist of several cells placed in series to give the required voltage as each cell is capable of providing an EMF of 2.1 volts.
In order to enable the basic lead acid cell to produce a voltage, it must first receive charge. The voltage applied to provide this must be greater than the 2.1 volts to enable current to flow into the cell. If it were less than this, charge would actually flow out of it.
Once charged, the cell or battery will be able to provide charge to external circuits, often operating over several hours dependent upon the drain on the cell or battery.
Lead acid battery self discharge
The self discharge characteristic of the lead acid battery is relatively good. At a room temperature of 20°C the self-discharge rate is around 3% per month> In theory a lead acid battery can be stored for up to 12 months without recharge. However at higher temperatures the self discharge is higher. At 30°C the self-discharge increases and a recharge will be needed after 6 months. Letting the battery drop below 60% for some time causes sulphation.
Sulphation is a process which reduces the capacity of lead acid batteries. During normal use, small sulphate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulphate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the active material within the cell and result in a reduction of capacity within the cell.
Lead acid battery advantages & disadvantages
Although lead acid batteries are widely used because they have a number of distinct advantages, they also have several major disadvantages. All these need to be considered when deciding upon whether to use this technology or not.
Lead Acid Battery Advantages
- Mature technology
- Relatively cheap to manufacture and buy (they provide the lowest cost per unit capacity for rechargeable cells)
- Large current capability
- Can be made for a variety of applications
- Tolerant to abuse
- Tolerant of overcharging
- Wide range of sizes and specifications available
- Many producers worldwide
Lead Acid Battery Disadvantages
- Fails after a few years use lifespan typically 300 - 500 cycles
- Cannot always be used in a variety of orientations
- Corrosive electrolyte (can cause burns to people and corrosion on metalwork)
- Lead is not environmentally friendly
- Acid needs disposing of with care
- Not suitable for fast charging
- Must be stored in charged state once electrolyte introduced
- Typical charging efficiency only around 70%
The lead acid battery is very well established. It has been in use for over 150 years and is currently one of the mainstays of the automotive industry. The lead acid battery has a high current capability, low cost and it is tolerance to abuse. This makes it ideal for many applications. However with the move to more environmentally friendly sources of power, electric vehicles now appear to be the future with manufacturers and legislation pointing to the phasing out of the internal combustion engine. For electric vehicles Lithium Ion technology provides better performance, they are more environmentally acceptable and they have the performance to enable electric vehicles to succeed. As such the lead acid battery is likely to be considerably less widely used.