BATTERY The battery is located in a well in the floor of the luggage compartment on Saloon models, beneath the rear seat cushion of the Estate Car, and behind the right hand seat on Van and Pick-up variants. It should be noted that while most Mini models will have a NEGATIVE earth electrical system, on early models prior to approximately October 1969, the system had POSITIVE earth polarity and it is important to observe the correct polarities for the respective systems as the various electrical components are affected by the earthing arrangements.
Electrolyte Level The level of the battery electrolyte in each cell should be checked periodically, and distilled water added if the level is below the separators, or the bottom of the fitting tube on through- fill type batteries. Do not over-flu the battery.
In some cases the battery case is translucent to allow the level to be checked without the need for lifting the vent cover.
It is good practice to run the car immediately after topping-up the battery, especially in cold weather, to ensure thorough mixing of the acid and water and so prevent freezing.
If the battery is found to need frequent topping-up, steps should be taken to discover the reason. For example, the battery may be receiving an excessive charge from the alternator, in which case the charging system charge rate should be checked.
If one cell in particular needs topping-up more than the others, check the condition of the battery case. If there are signs of acid leakage, the source should be traced and corrective action taken.
NOTE: The electrolyte level should not be topped-up within half an hour of the battery having been charged from an external source, lest it floods.
State of Charge The state of charge of the battery can be determined by checking the specific gravity of the electrolyte in each cell with a Hydrometer and measuring the voltage under load across the battery terminals with a heavy discharge tester. It is unlikely that the normal owner-driver will possess the latter piece of equipment, but a suitable hydrometer to test the specific gravity can be obtained quite cheaply from a motor accessory shop.
A specific gravity reading of at least 1.275 should be obtained if the battery is fully charged, or 1.120 if discharged. It is more important that the readings in each cell be equal, as a low s.g. in one cell indicates an internal fault and this will affect its ability to hold its charge.
If a heavy discharge tester is available, the output voltage of the battery can be tested as follows: The acid level in the battery must be correct before attempting to measure the voltage. Press the probes of the discharge tester firmly onto the battery terminals for about 5 to 10 seconds and read off the voltage indicated on the instrument scale. A reading of 12.6 should be obtained from a fully charged battery. If less than 8 volts, this indicates an internal fault in the battery.
Connections The battery terminals and leads should be kept clean to ensure good connections. Remove the battery if necessary to clean the terminals, but always detach the earth lead first.
If the battery posts or cable terminals are corroded, this can normally be removed by pouring boiling water over them, then brushing them with a wire brush.
When reconnecting the cables, apply a thin film of petroleum jelly or grease to both the terminals and posts. Tighten the terminals securely.
The battery earth strap and the engine earth strap should also be checked for proper connection and condition.