Lucas type ST X W9A, 12V, rated at 58 Ampere-hours for 20 hours, 'earthed on the positive side to prevent corrosion and increase spark intensity'
Check battery state at intervals (as described in notes below).
See notes below regarding voltage measurements.
Many owners have not secured the (modern) batteries within the battery tray - but care must be taken to ensure the leads are not allowed to fret.
Disconnect wiring and remove 2 nuts on retaining studs. Battery will now lift over the retaining studs.
An alternative (period) battery is the Lucas type SG9A.
Traditionally made lead-acid batteries have the bridges between the cells exposed and this makes the condition of the battery easy to test. The old style voltmeters that were used to test single cells, do not read up to 12 volts and are almost useless on modern batteries. Hence they are easy to obtain cheaply if you are still making the effort to maintain traditional batteries. Each cell should give a voltage of just over 2 volts if the battery is OK and faults are usually obvious, because all six cells should be the same.
Most owners have modern batteries fitted, which are more difficult to check, because you have to discover whether it is behaving as it should and not whether one cell of the battery is behaving in the same way as its neighbours.
Connect a voltmeter across the terminals and check for a 12.5 Volt reading. If less, charge the battery. If the battery voltage has fallen below 10.5 volts, it may be due to internal damage. Battery manufacturers recommend that a modern battery should be replaced if its voltage after charging and stabilising (standing for six or more hours) measures less than 12 volts.
If the voltage measurements taken when the battery is not under load are OK, then it may be wise to carry out further checks with the battery under load. Check the battery's ability to supply starting power by operating the starter motor with the ignition turned off. The voltage measured at the battery terminals should not fall to less than 10.5 volts. If it does, then the battery is supplying more current than it is capable of, due to either:
1) The battery is undersized (which may be a result of internal damage)
2) There may be a fault in the starter motor - check the starter motor switch contacts for burning and the starter motor for partial shorts.
Note that modern batteries are often rated in CCA - between 450 and 500 would be an appropriate replacement.
Lincon Batteries produce a traditional appearance battery for classic cars - part #291 seems to be a close match to the original.
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The rear N/S wooden floor panel contains a trap which is lifted by means of the above leather tag for access to the battery.
This tag is screwed to the trap.
A sketch of the battery tray and battery fixing studs with a suggested alternative method of securing modern batteries.
The original Lucas battery had special lugs, moulded onto the top of the battery ends with holes that allowed a pair of battery tray studs to go through them and hold the battery securely.