- on Education & Information
- Published in issue 11/2004 on page 0
Sealed Lead-Acid Batteries
SLAs still going strong
Lead-acid batteries still form an essential part of the on-board power systems in cars, motorcycles, boats and caravans. In its new form, featuring a fixed electrolyte and a sealed enclosure, this veteran battery technology (invented in 1850!) is now more versatile than ever.Sealed batteries with a fixed electrolyte have been in production for more than forty years. The electrolyte (dilute sulphuric acid) is fixed either using silica gel (lead-gel, or ‘dryfit’ battery) or using a glass fibre mat (AGM or ‘absorbed glass mat’ technology). This allows the oxygen produced at the positive electrode when the battery is overcharged to diffuse to the negative plate where it can recombine into water. This cycle of recombination makes the battery emit practically nothing in the way of gases, and so it can be built into a sealed enclosure. To prevent rupture in the event of the pressure getting too high, the cells (as in almost every sealed battery) are equipped with self-closing safety valves. The combination of fixed electrolyte and a sealed enclosure allows operation in any orientation (although AGM batteries must not be charged upside-down). The most important advantages of sealed lead-acid batteries, besides their low price, are their low self discharge, simple charging method, and long life, especially when continuously charged.