When Should You Not Jump-Start a Car Battery?
3 lessons in this series, 8 min in total
- When Should You Not Jump-Start a Car Battery? 2 min read
- How to Use a Jump Starter Safely: Step by Step 3 min read
- Does a Jump Starter Protect You If the Clamps Are Backwards? 3 min read
This lesson draws on AAA’s jump guide and battery brochure, NOCO’s GB40 guide and Clore’s JNC660 manual. See how we research.
Frozen battery: don’t jump it
NOCO’s GB40 guide, Clore’s JNC660 manual and AAA all say the same thing: never jump-start a frozen battery. AAA gives the reason. A frozen battery may rupture or explode when you try.
Freezing isn’t always obvious. AAA’s battery brochure names two signs to look for in cold weather: a bulging case, or ice in the cells. Check for both before the clamps come out.
If you find either sign, don’t connect anything. AAA suggests removing the battery and letting it thaw somewhere warm first. All three sources name a frozen battery as a reason to stop, so rule it out before anything else.
Cracked, leaking, wrong type or a damaged pack
AAA says to look for cracks, bulging sides or a strong rotten-egg smell, and to replace a battery that shows any of them rather than jump it. For the earlier warnings, see signs your car battery is dying.
Next, confirm the battery type. NOCO limits the GB40 to 12-volt lead-acid batteries (wet, gel, MF, EFB and AGM), and Clore the JNC660 to lead-acid. If you’re unsure of the chemistry or voltage, NOCO says not to jump it.
As for the pack, NOCO says to stop if the GB40’s casing is cracked, its cables are damaged, or its battery gets excessively hot, smelly or deformed. Clore says to have a JNC660 checked by a qualified service person after a sharp blow.
| Stop sign | Who says don’t jump | Do instead |
|---|---|---|
| Frozen | NOCO, Clore, AAA | Thaw or replace it |
| Cracked, bulging, leaking or rotten-egg smell | AAA | Replace the battery |
| Not 12V lead-acid, or unsure | NOCO, Clore | Don’t connect |
| Damaged pack | NOCO, Clore | Stop and have it checked |
Set up before you connect
- Protect yourself. Both manuals call for eye protection and no metal items such as rings and watches. Clore warns that a battery short can weld a ring to metal and cause a severe burn.
- No flames, good airflow. Lead-acid batteries give off explosive gas, so both manuals say not to smoke nearby and to work in a well-ventilated area.
- Ignition and loads off. Clore says to turn the ignition off before connecting. NOCO says to switch off loads such as headlights, radio and A/C before you try to start the car.
- Read the car’s owner’s manual. Both brands say so. Clore notes that some vehicle makers recommend an alternate jump point instead of the battery’s positive terminal.
Then move on to how to connect a jump starter step by step.
