• SolarKobo

Battery Life

Updated: Dec 27, 2019

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

  • Run-time

  • Shelf life and

  • Cycle life

Run Time

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 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.

Shelf Life

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.