Battery Cables

Made up battery cables from 2.5 mm2 to 95 mm2, and flexible cable by the metre.

Sizes run 2.5, 10, 16, 25, 35, 50 and 95 mm2. On the rough rule of 10 amps per mm2 of copper that is 25 amps at the small end and 950 at the top, and the figure for each one is on its own spec table. Made up lengths go from 10 cm up to 3 metres.

The eye terminals are soldered as well as crimped. That costs more to make and it is the reason they last: every connection adds resistance, and resistance on a high current DC circuit turns into heat and lost volts. The eyes are 8.2 mm and take up to an M8 bolt, which covers most battery posts and busbars on a system this size.

Buy a pair, one red and one black, for anything that needs a positive and a negative: battery to inverter, bank to busbar, controller to battery. Buy a single where you are only bridging one leg, which is usually putting a breaker, a shunt or an isolator into a circuit that already exists.

Heating is rarely what limits you. On a DC run it is the voltage drop over the length, so a cable that will never overheat can still be far too small for the job. A charging run wants about 1 percent voltage drop maximum or the battery never finishes its absorption stage. Battery to inverter about 2 percent maximum.

The flexible cable sold by the metre is welding type cable: a high strand count so it bends into tight spaces instead of fighting you, with the same copper cross section as anything else at that size. Two specialist cables sit here too, the cigarette lighter cables and the 40 cm Kontiki Seahorse torpedo lead.