Block heaters are used in somewhat milder climates as well – even though a modern ICE will start quite fine at even below -20°C (increasingly more unreliably th

Block heaters are used in somewhat milder climates as well – even though a modern ICE will start quite fine at even below -20°C (increasingly more unreliably the lower you go), doing so is somewhat harmful for the engine. (Also, by heating the engine fluids you can also blow some warmer air into the cabin to prevent the windows from frosting when you get inside – not to mention the added comfort.) Actual battery warmers are much rarer I think, but that isn't often an issue as long as you keep your battery well charged (and obviously have a more capable battery to begin with). The usual recommendation is to start using the block heater even before temperature gets below freezing (for convenience reasons not many people do so).