These are small, maintenance-free batteries which are sealed as the electrolyte is not depleted during operation. The electrolyte is absorbed in a porous separator or in a gel, so that the battery can be operated in different orientations without spilling. This allows the batteries to be used in portable devices.
The chemistry of these batteries is that of conventional lead-acid batteries. However, they have a unique characteristics. The oxygen generated on overcharge is recombined in the cell and there is no water loss. Indeed, oxygen reacts at the negative electrode:
This reaction is possible insofar as there is a very limited amount of electrolyte in the cell, this allowing quick gas diffusion between the plates.
Sealed lead-acid batteries are in both cylindrical and prismatic shapes. The cyclindrical ones (usually designed as SLA batteries) have excellent high-rate characteristics. Other than in portable devices, sealed batteries can be used in standby applications, e.g. telephone exchange stations, were they are kept in float charge. In this case too, oxygen recombination is possible.
Small lead-acid batteries lag behind other systems in terms of electrochemical performance. However, they have a notably high shelf-life and an attractive price.
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You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.