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Where to start when discussing a system?

All systems are made up of interrelated parts and it is usually difficult to relate to one part without considering the relationship to the others. For this reason it is often best to take an overview and then to gradually spiral downward into the relationships. I will try to proceed so in this and subsequent articles. However, as always, I ask that you
consider that this is written with the intent to be of service and without proof reading.

The typical motorcycle uses a 12-volt, lead-acid battery to provide electrical power when the bike's charging system is unable to provide sufficient power. The battery is of limited size and thus capacity due to weight and size constraints. Some bikes use a 6-volt rather than a 12 volt battery so perhaps a good beginning is to consider the difference in appearance and basic construction.

When viewed from above, a typical lead-acid battery will have a series of cell caps or plugs, which were used to fill the battery with the sulphuric acid (H2SO4) and water mixture called electrolyte. Each cell of a lead-acid battery (subsequently to be referred to simply as the battery) has a fully-charged voltage of about 2.1 volts. From this it can easily recognized that 2.1 volts times six cell caps = 12.6 volts. A six-volt battery will have three caps. Automotive batteries typically have their cell caps connected in threes but it is easy to recognize them by the shape of the caps and a sneak peek to the side of many will reveal three tubes from each long cap. Viewed from the side, the three cell walls can often be identified and usually individual cell plates and dividers within each cell.

Batteries require some means to prevent pressure building up inside the case due to heating and gasses that are produced by electrolysis. Automotive batteries usually provide venting through baffles in the cell caps. Due to the shaking, bouncing and tilting to which bike batteries are subjected, internal baffles are provided and a single vent tube is provided. This tube is typically connected to a drain hose which directs spilled electrolyte and corrosive gasses away from the bike.

One check that should be on everyone's list is to check the vent hose! The hose should be firmly in place on the battery's vent outlet tube, free of kinks, bends and other restrictions, and directed below the bike where any nasties will not land on expensive components.

What is 12 volt?
How is battery capacity indicated?
Positive and negative...

More in subsequent articles.