Batteries are a very important feature of most alternative power systems. The energy is stored in the batteries for use at a later time. The battery is a silent worker that delivers energy until it quits of exhaustion and old age. It is more prone to failure than most other parts in a system. Much is expected but little is given in return. With a shorter lifespan than the host device, battery replacement becomes an issue, and the lifespan of a battery is not necessarily fixed by the manufacturer. It is dependent on a number of factors, including its type, chemical changes in the battery, age, conditions under which it is used and how it is generally used.
Naturally, batteries wear out with age and use. However, it is therefore necessary for battery users to understand battery life and the factors that determine the lifespan of a battery so they can effectively manage performance. Keeping in mind the high cost of batteries and the short period that the manufacturer’s warranty covers the battery (Warranty periods for batteries last for just twelve months.), it is important to know the best battery choice for your power needs and how to effectively manage performance.
You can read all about inverter batteries and how to maintain them here.
Batteries have three distinct measures of life
Shelf life and
Run time refers to how long a battery or battery pack will run on a single use. This is not fixed for any battery and it also depends on the appliance on which the battery is run, but users can find a clue in the depth of discharge for each battery.
DEPTH OF DISCHARGE
Depth of Discharge is how much energy is discharged from the battery before it is charged to 100% again. For instance, a battery with 50% will have 50% of its energy capacity discharged, before it begins charging again. It also means that a battery can only be discharged at 50% and never below. Most inverters and chargers do this automatically. Otherwise, users should not use a battery below its depth of discharge.
Unless otherwise stated, the depth of discharge for most lead-acid batteries should never be less than 80%.
As seen in the chart below, the number of cycles yielded by a battery increases as the depth of discharge decreases.
Battery Shelf Life is the time an inactive battery can be stored before it becomes unusable. It is usually considered as having only 80% of its initial capacity. The conditions under which a battery is stored either by the dealer or the user will determine its shelf life and in turn, eventual lifespan.
Batteries are electrochemical devices which convert chemical energy into electrical energy or vice versa by means of controlled chemical reactions between a set of active chemicals. Unfortunately the chemical reactions on which the battery depends are usually accompanied by unwanted, parasitic chemical reactions which consume some of the active chemicals or impede their reactions even when not in use. Even if the cell's active chemicals remain unaffected over time, cells can fail because unwanted chemical or physical changes to the seals keeping the electrolyte in place.
The shelf life of a battery can be reduced in the following ways
The active chemical materials can be depleted over time.
The active chemicals may initiate unwanted reactions that can contaminate the active chemical materials.
Storing batteries under high temperatures seriously affects the battery life. The temperature under which the battery is ‘shelved’ affects both the shelf life and the lifespan as well as charge retention. Heat is the enemy of the battery. Even small increases in temperature will have a major influence on battery performance affecting both the desired and undesired chemical reactions. Generally, even under normal operating conditions, storage temperature effects can lead to premature failure of the cell.
For sealed cells, increased pressure can have a similar effect as high temperatures to wet cells. In fact, an increase in temperature will lead to an increase in pressure. High pressure can cause short circuiting of the cells, interruption of the path of the current, swelling of the cell casing or rupture of the cell casing. All this will reduce the potential battery life. For safety reasons, most batteries come with pressure release vents to provide a controlled release of pressure since manufacturers have no control over how the user treats the cells once they have left the factory.
It is therefore very important to purchase batteries from trusted dealers and to install them in well ventilated spaces. Also, before a battery is installed, ask to check for signs like swelling of the casing or any ruptures.
At SolarKobo, we offer our clients batteries that have been stored under the best possible conditions.
This is one of the key cell performance parameters and gives an indication of the expected working lifetime of the cell. To be able to define cycle life, we have to first define what a battery cycle is.
A charge cycle is the process of charging a rechargeable battery and discharging it as required into a load. A charge cycle means using all of the battery's capacity, but not necessarily by discharging it from 100% to 0%. In other words, the number of cycles for a rechargeable battery indicates how many times it can undergo the process of complete charging and discharging until failure or it starting to lose capacity.
The cycle life can then be defined as the number of charge and discharge cycles that can be achieved before a battery reaches the end of its useful life. Each charge and discharge cycle, is accompanied by a slow deterioration of the chemicals in the cell. Of course, the user will not be able to tell. But this depletion is mostly unavoidable though there are also other unwarranted chemical processes that go on inside the cells.
Cycle Life depends on the following
Depth of Discharge
As stated above, cycle life decreases with increased Depth of Discharge (DOD). In fact, many inverters will shutdown when their batteries are being discharged below their depth of discharge because the batteries may be permanently damaged if fully discharged. Deep discharge inevitably lower the lifespan of a battery.
Batteries emit a corrosive and explosive mix of hydrogen and oxygen gases during the final stages of charging, which when accumulated in large quantities can ignite if exposed to a flame or spark. They must be installed in a well-ventilated enclosure, preferably away from the house.
Also, the batteries get heated up during use. It is advised that they are installed in airy places for cooling. As batteries have provisions for water to cool them, installing them in well ventilated places reduces the frequency of the water-topping requirement.
The batteries are to be installed at places where children cannot reach them or where there is not much disruptive domestic activities.
The area in front of the installation space should be reserved as work space and not used for storage of any kind. Operators should be able to walk up to the inverter equipment without any obstruction.
Have clear instructions laminated and posted on the wall beside the installed system where in your absence, another operator, a friend or family member, may want to use the system.
Advisably, the inverter system if not mounted on the wall should be installed atop a metal rack. In most cases, SolarKobo requires this as a standard installation procedure.
The batteries should be installed properly and by professionals.
The current and voltage with which a battery is charged affects its lifespan. Overcharging damages batteries. Many inverter systems come with intelligent chargers that regulate the current and voltage that charge the batteries.
A good charger for your batteries should be able to
Deliver a clean regulated voltage output with little or no spikes, ripple, noise and radio frequency interference (RFI) all of which could cause problems for the battery or the circuits in which it is used.
Also, when a charger is initially switched on to an empty battery, the charging current could be considerably higher than the maximum specified charging current. A good charger must therefore be able to limit this rise.
Also, there can be energy losses in the batteries. It is thus, good to use charges that have very high efficiencies.
Our engineers at SolarKobo advice against the use of generators. Batteries can be charged from the AC mains, solar panels or other batteries.
Read all about charge controllers here.