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Rover 400 series Battery Testing

Apart from physical defects, the most likely indication of a defective battery would be a difficult starting of the car. Slow cranking is immediately identifiable, this may be first noticed after driving at night, or with the headlights/window wipers on.
If the battery seems weak or fails to crank the engine normally, the charge may be low due to a number of reasons not just a defective battery.

To find the battery's "charge state." a multi meter or voltmeter is normally required, tests can also be made with a hydrometer. The battery fitted to 416 automatic model and many replacement batteries have built in battery condition indicator.

Multi meter/Voltmeter Test

Using a Multi meter on DC Volts, or a DC Voltmeter the open terminal voltage of the battery needs to be tested.
With the vehicle negative lead to the battery disconnected, or the battery completely removed from the vehicle, measure the open circuit voltage by connecting the Multi meter/Voltmeter leads across the terminals of the battery.

A reading of 12.66 volts or above indicates a fully charged battery.

Approximate charge Terminal Voltage
100% 12.66V
75% 12.45V
50% 12.24V
25% 12.06

Hydrometer Test

This can only be done if there is access to the battery cells, and this in turn will depend on the manufacturer of the battery. When testing some Maintenance free Batteries the sealing caps may be located under the top label.

It is advisable to wear safety goggles and rubber gloves when performing tests on any lead acid battery.
Using a suitable tool, open the cover on the battery cell. Squeeze the bulb of the hydrometer then insert the tube part into the liquid of the cell, release the bulb to draw liquid into the body of the hydrometer.
Draw liquid into the hydrometer until you see the float in the body (usually a colored plastic ball or glass bulb) rise, read the value on the gauge or scale of the hydrometer, Squeeze the bulb to release the liquid back into the cell.

Approximate charge Relative acid density
100% 1.265 g/cm³
75% 1.225 g/cm³
50% 1.190 g/cm³
25% 1.155 g/cm³

Repeat the process for all of the cells in your battery, noting the measurement.

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