A good battery is essential for reliable starting, especially during cold weather because cold weather increases the cranking load on the battery. Oil gets thicker at low temperatures so it takes more amps to crank a cold engine when you try to start it. At -20 degrees C, the number of cranking amps it takes to start a cold engine may increase as much as 2X. At -27 degrees C, it can take 3X or more amps to crank the engine depending on the viscosity of the oil in the crankcase. The thicker the oil, the harder is it to crank the engine.
At the same time, cold temperatures also sap the battery’s ability to supply amps. At 0 degrees C, most batteries can only deliver about 65% of their normal cranking amps. At -20 degrees, battery power is cut in half!
Warning: Do NOT attempt to recharge your battery if it has run down and the liquid inside is frozen. This may cause the battery to explode! Remove the battery and take it inside so it can thaw before recharging or testing it.