Batteries – Maintenance and Testing – What to Check


Any and all maintenance should be undertaken by a trained engineer.

bad-batteries1. Always keep battery top and terminals clean.

2. Coat terminals and connections sparingly with petroleum jelly or similar.

3. Keep terminals tight, but NEVER over tighten.

4. Check regularly that electrolyte is 3 mm (1/8”) to 6 mm (1/4”) above the top of the plates. If topping up is required, use only distilled water or chemically pure water.

5. Check alternator/generator belt regularly for signs of wear and ensure it is tensioned to manufacturer’s recommendations.


Before testing battery with instruments, always make a visual examination.

1. Corroded terminals – a white powdery substance around post connections which may prevent battery charging.
2. Check that all cells contain electrolyte. A dry cell indicates a cracked casing.
3. Check for loose terminals and any other external damage.

Hydrometer Testing
Use a hydrometer to establish the specific gravity of the sulphuric acid in the battery, and as a result of the state of charge.

1. Do not add distilled water.
2. Keep the barrel upright, draw up enough electrolyte from each cell in turn to allow the float to ride free. If necessary, tilt the battery to obtain sufficient electrolyte. Read off at eye level.

1.270 to 1.280 S G Full Charge
1.220 to 1.230 S G Half Charge
1.150 to 1.220 S G Discharged

The readings from all cells should be within 0.030 points.
If the variance is greater, then it is likely that the battery needs replacing.

If all cells are consistently low the battery may still be serviceable, but we advise REPLACEMENT as quickly as possible.

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