The battery is the foundation of the entire electrical system, and the correct specification is more important on the Midget than on most cars because both the polarity and the physical terminal layout changed during production. Two battery sizes were used: one specification for the 1275cc, and a different specification for the 1098cc and the 1500. The chassis number and engine type must both be confirmed before ordering to ensure the correct physical size, polarity, and terminal layout are supplied.
Terminal Layout and Polarity
Pre-November 1967 cars are positive earth with the positive terminal connected to the body. From November 1967 (GAN4-60460 / HAN9-72041) onward, cars are negative earth with a different terminal layout. When the 1500 was introduced, the terminal layout changed again, the car retained negative earth, but the terminals had to return to their original positions because the Triumph engine has its starter motor on the left side of the engine, opposite to the A-Series starter on the right. A battery with the incorrect terminal layout may physically fit the battery tray but will require the cables to cross over each other, creating a potential short circuit against the battery clamp or adjacent metalwork.
Battery Clamps and Tray
Battery clamp kits differ between positive earth and negative earth cars, so the correct kit must be specified when ordering. The battery tray sits in the boot behind the rear bulkhead and should be inspected for corrosion at every service, acid spillage from the battery is one of the most common causes of boot floor corrosion.
Battery Cables
Battery cables differ between production periods, reflecting the changes in terminal layout and earth point location. The body earth point for the battery is on the left side of the bulkhead on chrome-bumper cars and on the right side of the bulkhead on rubber-bumper cars. When the correct battery is fitted, the terminals should be nearer the bulkhead than the heater, if they are the wrong way round, the cables will not reach their connection points without crossing.
Earth Strap
The earth strap is one of the most commonly overlooked maintenance items on any classic car, and on the Midget it is responsible for a disproportionate number of electrical problems. A corroded or loose earth strap connection creates resistance in the earth return circuit that affects every electrical component on the car, dim headlamps, slow starter cranking, erratic gauge readings, and flickering interior lights can all be caused by a single poor earth connection. The strap and both of its connection points (battery terminal and body mounting bolt) should be cleaned to bright metal and tightened securely at every service. The engine earth cable connecting the engine block to the body should be checked at the same time.
Battery Chargers and Conditioners
Battery chargers and intelligent conditioners are essential for cars stored for extended periods between outings. A conventional trickle charger maintains a constant low current that can overcharge the battery if left connected indefinitely. An intelligent conditioner monitors the battery's state of charge and adjusts its output accordingly, maintaining the battery at optimum charge without the risk of overcharging. A battery left in a discharged state for even a few weeks will suffer sulphation, a chemical process that permanently reduces the battery's capacity.