Since cyclists' legs are most efficient over a narrow range of pedaling speeds, or cadence , a variable gear ratio helps a cyclist to maintain an optimum pedalling speed while covering varied terrain. Some, mainly utility, bicycles use hub gears with between 3 and 14 ratios, but most use the generally more efficient dérailleur system, by which the chain is moved between different cogs called chainrings and sprockets in order to select a ratio. A dérailleur system normally has two dérailleurs, or mechs, one at the front to select the chainring and another at the back to select the sprocket. Most bikes have two or three chainrings, and from 5 to 11 sprockets on the back, with the number of theoretical gears calculated by multiplying front by back. In reality, many gears overlap or require the chain to run diagonally, so the number of usable gears is fewer.
There are situations when the compartment of the battery is not at horizontal position and it has been designed for slightly vertical position. Before buying the battery you must be sure about the position of your battery compartment as the wet-cell batteries are not recommended for any other complicated positions as there is risk of acid spilling; whereas gelled, lithium or AGM marine batteries can be placed virtually at any position except upside down as it might damage the internal elements of the battery. If the position is not horizontal then it’s better not to go for a flooded battery.