These are also known as Valve Regulated Lead Acid (VRLA)
batteries. These batteries are the most popular for usage with UPS systems for computer or commercial application. Being sealed, these batteries do not emit any fumes and hence can be very well installed next to electronic equipment. These batteries also can be housed in a close enclosure if necessary. These batteries are also maintenance free and avoid any hassles of checking specific gravity, adding water or acid, etc. These batteries have a relatively lesser life of approx. 3-5 years. The life expectancy typically depends on the number of charge/discharge cycle experienced by the batteries and the ambient temperature in which the batteries are used. These batteries are primarily the most popular for commercial applications due to “Install and forget” approach
Permissible operating temperature range of SMF batteries is 15 deg C to 50 deg C, but using within an operating range 5 C to 35 C will extend service life. Below – 15 deg C, the battery changes its chemical composition and cannot hold a charge. You will enjoy longer service life, if batteries are operated in ambient temperature range of 20 deg C to 25 deg C (68F to 77F). At lower temperature they have longer life and lower capacity while at higher temperature they have higher capacity and lower life.
A good rule of thumb when determining battery service life in relation to temperature is that for every 8.3 deg C (15F) average annual temperature above 25 deg C (77F), the life of the battery is reduced by 50%. Therefore warranty of the battery should be ideally reduced to 50% for every 8.3 deg C (15F) increase in operating temperature above 25 deg C (77F).
SMF batteries are designed to have a float voltage of 2.3 V/cell. This means that a 12 V battery (with 6 internal cells) has a float voltage of 13.8 Volts. Most of the battery manufacturers recommend float voltage of 2.25 – 2.3 volts per cell. When there are more cells (generally >120) in series, to compensate for higher temperatures, float voltage should be decreased by approx. 3 mV per cell per deg C above 25 deg C. It should be increased by the same amount when operated at a temperature less than 25 deg C to avoid undercharge. The Cutoff voltage is 1.67 V/cell for high rate of discharge
It is recommended that SMF batteries should not be left in totally discharged state more than 72 hrs. The batteries may get partially or fully damaged due to SULPHATION if charging does not start within 72 Hrs from totally discharged state. Sulphation is the formation of lead sulphate on negative plates which acts as an insulator and has a detrimental effect on charge acceptance