All MGAs use a 12-volt Lucas positive-earth electrical system, supplied by two 6-volt batteries connected in series mounted in cradles on the chassis frame behind the seats. This rear-mounted twin-battery arrangement is unique to the MGA among common classic British sports cars and creates a set of battery and cable requirements distinct from the single-battery engine-bay layouts used on the MGB and Midget. Cables run forward under the car from the rear-mounted batteries to the starter motor at the front of the engine; earth connections have to be made cleanly to the chassis, engine block and bodywork; and the two 6V batteries have to be paired correctly and held securely in their cradles under the hood stowage floor.
6-volt batteries
Two 6-volt batteries are required, one for each cradle position, connected in series to give the 12-volt supply. Batteries are stocked both individually (a single 6V battery, useful when only one of the pair has failed) and as a matched wet pair (two 6V batteries supplied together, the correct starting point for a full battery replacement). Both batteries should be of the same age and state of charge for best service life; replacing only one battery of a pair that has seen extended service will give shorter overall life than replacing both together, as the older battery will pull the new one down. The modern wet-cell batteries stocked by MGOC are supplied with a suitable cold-cranking rating for the MGA's starting requirements across all variants.
Battery hold-down and cradle hardware
Each 6V battery sits in a cradle on the chassis frame and is secured by J-bolts and a top clamp strip, the factory arrangement, where angle-iron clamps are drawn down onto the battery top by threaded rods hooked into holes in the cradle frame. Battery clamps are stocked in both standard steel and stainless steel finishes; the stainless option resists the sulphuric fume corrosion that attacks standard steel clamps over years of service. Short battery clamp bolts and J-bolts are stocked as service items to replace originals that have corroded or seized.
Battery cables, MGA-specific
The MGA's rear battery location means the main starter cable is considerably longer than on engine-bay-battery cars. MGOC stocks an MGA-specific starter cable routed to the correct length and terminal specification. A battery link cable connects the two 6V batteries in their cradles to form the 12V series pair; this is a short, heavy-gauge cable with matched terminal ends. Earth cables are stocked for the two critical earth paths: battery to body (main chassis earth return from the battery positive terminal) and engine to body (the short earth strap that keeps the engine block electrically bonded to the chassis despite the rubber engine mounts that isolate it mechanically).
The battery-to-solenoid cable connects the battery supply to the starter solenoid at the front of the engine. Rubber battery terminal boots are stocked to prevent accidental shorting across the terminals when tools are dropped near the batteries.
Battery master switches
Two battery master switch options are stocked: a standard battery master switch for general road use, and an FIA-specification battery master switch for motorsport applications where a competition battery cut-off is required by the regulations. The master switch fits into the battery supply line and allows the car's electrical system to be isolated completely, useful during long-term storage, during electrical service work, and as a security feature. A Disconnect Battery Isolator is also stocked for simpler installations.
Replacement keys for both the standard and FIA master switches are stocked as service items.
Battery conditioning, Bat-Aid
Bat-Aid is a battery conditioning product stocked for cars that spend time standing between uses. Classic cars driven seasonally or occasionally are prone to battery sulphation, the chemical condition that develops in a battery held at less than full charge for extended periods, and Bat-Aid helps mitigate this, extending battery service life for cars not in daily use. A dedicated battery charger or conditioner is covered separately under the Battery Chargers & Conditioners node.
Ordering considerations
For a full battery replacement, the wet pair option provides two matched batteries in a single order. For partial replacement, individual 6V batteries are available. Battery cables are MGA-specific and stocked for pushrod cars. Master switch fitment is optional on road cars but strongly recommended for any car kept in long-term storage.
Battery clamps, J-bolts and terminal boots are common service items shared across all MGA variants.