The battery is a single 12-volt unit in an open box on the bulkhead engine-bay side, feeding the positive earth system through heavy-gauge cables to the starter switch, starter motor, and chassis earth. The TD and TF do not use the twin 6-volt arrangement of the later MGA. This section is divided into Batteries and Cables (battery, acid, four heavy-gauge cables, wood tray, stay, insulating cap), Battery Chargers and Conditioners (for storage or intermittent use), and Upgrades and Alternatives (isolators, master switches, booster cables).
Battery Specification and Polarity
All TD and TF cars left the factory with 12-volt positive earth, the positive terminal connects to the chassis. The battery is the same unit regardless of polarity; the surrounding components (dynamo, control box, ammeter, coil, fuel sender, electronic accessories) determine polarity. When converting earth, the battery is turned around in its tray and cables reconnected, but the polarity-sensitive components must match the new configuration.
Dry-Charged Supply
Replacement batteries are supplied dry-charged: the lead plates have been factory-charged but the battery is shipped without electrolyte. To activate, the battery is filled with sulphuric acid electrolyte at the point of installation.
This arrangement extends shelf life, a wet battery in storage gradually self-discharges and sulphates, whereas a dry-charged battery remains in factory condition until activated. A 1kg bottle of battery acid is supplied separately, with six bottles typically required to fill the battery to the correct level.
Battery Cables
Four cables make up the TD/TF battery installation: positive (earth) battery-to-chassis, negative battery-to-starter-switch, negative starter-switch-to-starter-motor, and positive (earth) engine-to-chassis providing the engine block earth path. Cable terminations and routings are TD/TF-specific. A rubber insulating cap protects exposed terminals against accidental shorts, particularly important on a positive earth car, where the chassis is positive and any metal bridging between the live (negative) terminal and chassis creates a direct short with fire risk.
Battery Tray and Stay
The battery sits in an original-pattern wood tray that provides a non-conductive base and protects the metal bulkhead shelf beneath from acid attack. The battery is held in place by a clamp-type battery stay, secured by two J-bolts that hook into the battery box, with associated nuts and washers. The complete J-bolt and nut set is available as a service kit. The tray and stay are the key items to inspect when restoring a TD or TF, corroded battery boxes are a common source of bulkhead damage caused by historic acid spills.
Battery Maintenance and Conditioning
A battery conditioner is recommended for cars in intermittent use. The 12-volt system with dynamo charging is vulnerable to discharge during storage, and a flat battery progressively sulphates. An automatic conditioner permanently connected monitors charge state and maintains it only when needed. Conventional 6/12-volt and 12-volt-only chargers are available alongside the multi-stage Accumate conditioner (suitable for batteries up to 55Ah, with ring and clip cables).
Battery Isolators and Master Switches
A battery isolator switch, fitted directly to the battery terminal post, disconnects the entire car from the battery at the turn of a knob, with a bypass fuse to keep the clock and any other essential standing loads alive. This is a useful safety feature for cars stored for long periods or transported on trailers, and provides immediate isolation in the event of an electrical fault. Master switches in standard and FIA (motorsport-approved) types are also available, the latter required by competition regulations for certain events.
Booster Cables
A pair of heavy-duty booster cables is a sensible addition to the TD or TF tool kit, the inertia starter motor draws significant current at the moment of engagement, and a tired battery on a cold morning is a familiar TD/TF starting condition. Booster cables allow assistance from another vehicle without disturbing the original battery installation.
Ordering Considerations
The battery itself is the same unit regardless of polarity, only the cable connections change. Specify positive earth (factory) or negative earth (if converted). Battery acid (six 1kg bottles for fresh activation) is supplied separately from the dry-charged battery. Cables are individual items rather than a kit, allowing damaged cables to be replaced individually.
Tray, stay components, J-bolts, and nuts are available individually.