Can You Leave a Jump Starter in Your Car?
4 lessons in this series, 11 min in total
- How Long Does a Jump Starter Hold a Charge? 3 min read
- Can You Leave a Jump Starter in Your Car? 3 min read
- Should You Keep a Jump Starter Plugged In? 2 min read
- Do Jump Starters Work in Cold Weather? 3 min read
This lesson draws on NOCO’s and Clore’s manuals, ASU’s hot-car study, Battery University’s BU-702 and AAA via CBS News. How we research explains the method.
What the manuals allow
Manuals give a storage range, for a pack sitting unused, and a narrower charging range, for safely taking a charge.
- NOCO GB40 and GB70: store at -4°F to 122°F (-20°C to 50°C), with a daily average of 32°F to 77°F (0°C to 25°C), indoors when not in use, and never above 176°F (80°C) under any condition. They operate in that same range but charge only at 32°F to 104°F (0°C to 40°C).
- Clore JNC660: ideal storage is 68°F (20°C), and not below 50°F (10°C) for best jump-starting. Its small battery is more temperature-sensitive than a car battery, and above 70°F (21°C) its amperage output drops.
How hot a parked car gets
In a 2018 ASU study in Tempe, cars parked in the sun on days of 100°F (38°C) and up averaged 116°F (47°C) inside within an hour. Dashboards averaged 157°F (69°C), and shaded cabins still came close to 100°F (38°C).
The study measured cabins and surfaces, not trunks. Even so, sunny dashboards averaged well past the 122°F (50°C) top of NOCO’s storage range, not far below its 176°F (80°C) never-exceed limit. Shaded cabins sat far above the 77°F (25°C) top of its daily-average range. Battery University lists a car dashboard or hot sun as unfavorable spots for a battery.
Heat also speeds up a stored pack’s slow drain: Battery University says self-discharge typically doubles with every 18°F (10°C) rise (see how long a jump starter holds a charge).
If you also keep a dash cam on the windshield, supercapacitor vs battery dash cams covers which kind copes better with a hot car.
Heat costs capacity for good
Battery University estimates how much capacity a fully charged battery can recover after a year of storage:
| Storage temperature | Lead-acid, full charge | Lithium-ion (Li-cobalt), full charge |
|---|---|---|
| 32°F (0°C) | 97% | 94% |
| 77°F (25°C) | 90% | 80% |
| 104°F (40°C) | 62% | 65% |
| 140°F (60°C) | 38% after 6 months | 60% after 3 months |
These are general figures, not results for these jump starters, but the pattern is plain: a year at 104°F (40°C) leaves 62-65%, against 94-97% at 32°F (0°C). The hotter the storage, the more capacity is gone for good.
Winter: slower drain, weaker car battery
Cold is gentler on a stored pack, as the table shows. The winter problem is power. AAA’s Dan Cave told CBS News Philadelphia in 2018 that a car battery loses about 35% of its battery life at 32°F (0°C) and about 60% at 0°F (-18°C).
That’s the car’s battery, not the pack, but it means cold mornings are when you’ll most likely need a jump (why a weak battery shows up in cold weather).
- Recharging: NOCO’s packs aren’t rated to charge below 32°F (0°C), so warm one indoors after a freezing night before recharging.
- Frozen batteries: both makers say to never jump a frozen battery.
Store the pack indoors if you can, then read should you keep a jump starter plugged in and the roadside emergency kit checklist.
Sources
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- NOCO GB40 user guide and warranty (PDF)
- NOCO GB70 user guide and warranty (PDF)
- Clore Automotive JNC660 operator’s manual (PDF)
- Arizona State University: Hot cars can hit deadly temperatures in as little as one hour
- Battery University BU-702: How to store batteries
- CBS News Philadelphia: Cold weather crippling car batteries (AAA)
