How-to guide · Jump Starters
How to Choose a Jump Starter for Your Engine Size
Engine ratings matter more than peak amps. Here is how to read a jump starter's rating and pick the right size for your car or truck.
By Watt Versus Editorial· Updated · 5 steps
This page was drafted with AI assistance from manufacturers' specs and manuals, and is checked by our editor.
Peak amps are the number on the box, but they are measured differently by different brands. The more useful rating is the engine size the manufacturer says the unit can start, given separately for gasoline and diesel. NOCO, for example, rates each Boost model by maximum gasoline and diesel displacement.
Why diesel ratings are lower
Diesel engines use higher compression and need more current to crank, so the same jump starter is rated for a smaller diesel than a gasoline engine. NOCO's GB40 is rated for 6.0 L gasoline but only 3.0 L diesel.
Cold weather
Batteries deliver less current in the cold and engines are harder to turn over. If you live where winters are hard, pick a model rated well above your engine size.
Step by step
- 1
Find your engine size and fuel
Look up the displacement in liters in the owner's manual or on the under-hood sticker, and note whether it is gasoline or diesel.
- 2
Match it to the rating
Choose a jump starter whose rating for your fuel type is above your engine's displacement.
- 3
Add a margin for cold
In cold climates, or for an older battery, step up one size.
- 4
Check battery compatibility
Most lithium jump starters are made for 12-volt lead-acid batteries. Check the manual before using one on a lithium starter battery or a 24-volt system.
- 5
Look for the safety features
Spark-proof clamps and reverse-polarity protection prevent damage if you connect the clamps the wrong way round.
Frequently asked questions
- How many amps do I need to jump start a car?
- Go by the engine rating rather than amps: pick a starter rated for your engine's displacement and fuel type, with a margin in cold climates.
- Can a jump starter for gas engines start a diesel?
- Only if the diesel is within its diesel rating, which is always lower than the gasoline rating.
- Is a bigger jump starter always better?
- It covers more engines and gives more starts per charge, but it is heavier and slower to recharge. Pick the size that covers your engine with some margin.