Closing Comments 7 . Introduction Batteries are perhaps the most expensive form of energy used, a standard AA cell can just about boil a tenth of a cup of water. Over 20,000,000,000 batteries are disposed of each year. Using these cells the best and most efficient way is essential. This can be defined as how much a cell can supply and for how long.
All cells have some internal resistance.
As cell sizes increase there internal resistance decreases, due to larger conducting surfaces. As cells become discharged the resistance also rises, so a cell which has failed in a high current application will still work for some time in a lower current application. Lower internal resistance means longer life and higher current. Applications which take little current like smoke alarms, will often use the battery for over a year and failure can be due to the time it has been used for and not the current drawn. These are the cheapest cells available and have changed very little since there invention in 1860.