Will My Car Start Tomorrow?

Q: What temperature is too cold for a car battery?

There is no single cutoff, but below -25C even good batteries struggle, and below -30C a weak battery often fails. A block heater helps a lot below -15C.

Q: Should I plug in my block heater tonight?

If the overnight low will drop below -15C and you have a block heater, yes — plug it in 2-3 hours before you need the car, or use a timer.

Tomorrow's overnight low, your battery's age, your car's age — one straight answer about tomorrow morning.

Tomorrow morning is the worst time to find out your battery is weak. This tool checks tomorrow's overnight low for your town, weighs it against your battery's age and your car's age, and gives you a straight answer: low, medium or high risk — plus what to do about it tonight.

City, town or postal code How old is your car battery? How old is your car?

No forecast for your town? Enter tomorrow's low manually instead.

How the risk is worked out

Three things decide whether your car starts on a cold morning, and the score adds them up (0 to 6 points):

Tomorrow's overnight low (0–3 points). Above -10°C scores 0. Below -10°C scores 1, below -20°C scores 2, below -30°C scores 3. Cold slows the chemical reaction inside a battery — at -20°C a battery can lose up to half its power, right when thick cold oil makes the engine harder to turn over.
Battery age (0–2 points). Under 3 years scores 0, 3–5 years scores 1, over 5 years scores 2. Most car batteries last 4–5 years. If you don't know the age, we score 1 and you should check the date sticker on the battery itself.
Car age (0–1 point). Over 10 years adds 1 point — older starters, wiring and worn parts make cold starts harder.

0–1 points is Low risk, 2–3 is Medium, 4–6 is High. The score is an honest estimate, not a promise — a battery test at a parts store (usually free) tells you more than any calculator can.

Frequently asked questions

Will my car start in -20°C?

Usually yes, if the battery is healthy and under 4–5 years old. At -20°C a battery can lose up to half its power, so an older battery is the risk — get it tested free at a parts store.

What temperature is too cold for a car battery?

There is no single cutoff, but below -25°C even good batteries struggle, and below -30°C a weak battery often fails. A block heater helps a lot below -15°C.

How do I know if my battery is too old?

Check the date sticker on the battery itself. Most car batteries last 4–5 years. Slow cranking on cold mornings is the first warning sign.

Should I plug in my block heater tonight?

If the overnight low will drop below -15°C and you have a block heater, yes — plug it in 2–3 hours before you need the car, or use a timer.