Best 12-Volt Battery Jump Packs and Maintainers for EVs and Generators

We earn a commission if you buy through links on this page, at no extra cost to you. It does not change what we recommend — see our affiliate disclosure. As an Amazon Associate I earn from qualifying purchases.

Every EV still has a 12-volt battery, and it does one job nothing else can: it powers the computers that close the contactors connecting the high-voltage pack. If the 12 V battery goes flat, the car won't wake, unlock normally or charge, however full the traction battery is. Electric-start portable generators rely on a small starting battery in the same way. There are two tools for this: a portable jump pack to wake the car, and a smart maintainer to keep the battery charged while the car or generator sits.

Battery chemistry decides what you can connect, and the makers are specific about it. Lead-acid, AGM and lithium 12 V batteries charge at different voltages and aren't interchangeable. Some EVs use a lithium low-voltage battery. Tesla's Model Y manual, for example, says cars built at Fremont after about December 2021 have a lithium-ion low-voltage battery with its own jump procedure. Some jump packs are rated for 12 V lead-acid only. A multi-chemistry maintainer needs the right mode selected, and its lithium mode may only cover batteries with a built-in BMS or four-cell LiFePO4. Read the spec, not the box art.

The owner's manual always overrides anything here. It tells you which 12 V battery the vehicle has, where to connect (many EVs use dedicated jump posts rather than the battery terminals) and in what order, and whether the maker allows an external charger or maintainer at all. Never use an EV to jump-start another vehicle unless the manufacturer explicitly allows it. Tesla, for example, says Model Y cannot be used to jump another vehicle. Once the car is awake, its DC-DC converter takes over recharging the 12 V battery.

For a generator, check the manual for the starting battery's voltage, chemistry and amp-hour size before connecting a maintainer. A small battery needs a maintainer rated for its size, not a car charger's bulk current.

How we picked

The maker explicitly lists your battery's chemistry (lead-acid, AGM or lithium) as compatible
Spark-proof clamps and reverse-polarity protection
Maintainers: a separate charge mode for each chemistry, and a rated amp-hour range that covers your battery
Jump packs: an engine and temperature rating that matches where and when you'll use it
Safety listing from a recognized testing lab, and a published warranty

We do not accept payment for placement and we do not publish star ratings we did not measure. Specifications come from each manufacturer's published spec sheet.

Side by side

Product	Type	Best for	Protection	Warranty	Operating temperature	Battery types	Capacity	Dead batteries	Input	Compatible batteries	Engine rating	Internal battery	Certification
NOCO GENIUS5	Smart charger / maintainer	Keeping a car-sized 12 V battery charged during storage, whatever its chemistry	Spark-proof, reverse polarity, short-circuit, open-circuit, overheating, overcharge	3-year limited	-4°F to 104°F (-20°C to 40°C)	Wet, Gel, MF, CA, EFB, AGM, Lithium	Charges up to 120 Ah; maintains all battery sizes	Detects down to 1 V; Force Mode for batteries below 1 V	120–240 V AC, 75 W max	—	—	—	—
NOCO Boost Plus GB40	Jump pack — lead-acid 12 V only	Waking a car with a flat 12 V lead-acid or AGM battery without a second vehicle	Spark-proof, reverse polarity; Manual Override for batteries below 2 V disables both	1-year limited	-4°F to 122°F (-20°C to 50°C)	—	—	—	—	12 V lead-acid only (NOCO: not suitable for any other battery type)	Gas up to 6.0 L, diesel up to 3.0 L	24 Wh lithium-ion	—
Battery Tender Jump N Start 1500 Amp Lithium Jump Starter (030-2020-WH)	Jump pack — lists lithium compatibility	A jump pack whose maker lists lithium 12 V batteries as compatible	Spark-proof smart clips, reverse polarity, short-circuit, over-current, over-temperature	1-year limited	32°F to 104°F (0°C to 40°C) per the manual	—	—	—	—	AGM, GEL, Lithium, Standard (sealed or flooded lead-acid), per Battery Tender's product page	12 V gas up to V8; diesel up to 5.5 L in Battery Tender's FAQ (its product description says 7.0 L)	12,000 mAh lithium	cETLus (UL 2743), UN38.3
Battery Tender Junior Multi-Chemistry 12V (022-0199-DL-WH)	Small-battery maintainer	Small 12 V starting batteries, such as a generator's, that sit between uses	Spark-free clips, reverse polarity, short-circuit	5-year limited	—	Six-cell lead-acid/AGM (flooded, AGM, GEL, sealed maintenance-free) or four-cell LiFePO4, selected by button	3 Ah to 30 Ah at 12 V	Won't start below 3 V; LiFePO4 recovery mode for 4–8 V batteries (3-hour limit)	120 V AC	—	—	—	ETL / cETL

The picks

#1 · Smart charger / maintainer

NOCO GENIUS5

Check price at NOCO

A 5-amp smart charger and maintainer for 6 V and 12 V batteries, with separate modes for flooded or maintenance-free lead-acid, AGM, and 12 V lithium (including LiFePO4) batteries that have a built-in BMS.

Best for: Keeping a car-sized 12 V battery charged during storage, whatever its chemistry

Charge current: 5 A DC
Battery voltages: 6 V and 12 V
Battery types: Wet, Gel, MF, CA, EFB, AGM, Lithium
Charge modes: 12V (14.5 V), 12V AGM (14.8 V), 12V Lithium (14.6 V, BMS-equipped batteries only), 6V, Repair, Force
Capacity: Charges up to 120 Ah; maintains all battery sizes
Dead batteries: Detects down to 1 V; Force Mode for batteries below 1 V
Protection: Spark-proof, reverse polarity, short-circuit, open-circuit, overheating, overcharge
Housing: IP65
Operating temperature: -4°F to 104°F (-20°C to 40°C)
Input: 120–240 V AC, 75 W max
Warranty: 3-year limited

A dedicated 12V Lithium mode as well as lead-acid and AGM modes, so one charger covers the chemistries an EV or generator might use
5 A charges a car-sized battery up to 120 Ah, and NOCO says it maintains batteries of any size, so it can stay connected for storage
Spark-proof, with reverse-polarity protection that stops it from sending current until the clamps are on the right way

You pick the mode yourself, and the wrong one is the wrong charge voltage. NOCO says the lithium mode is only for 12 V lithium batteries with a built-in BMS
Repair mode drives up to 16.5 V and is for lead-acid only. NOCO says to disconnect the battery first, so never use it on a battery still connected to an EV
It can't tell you whether your carmaker allows an external charger on the 12 V battery. Only the owner's manual can

Read the full write-up →

#2 · Jump pack — lead-acid 12 V only

NOCO Boost Plus GB40

Check price on Amazon(paid link)

A compact lithium-ion jump pack rated at 1,000 peak amps for 12-volt lead-acid batteries, with spark-proof clamps, reverse-polarity protection, a USB power bank and a flashlight.

Best for: Waking a car with a flat 12 V lead-acid or AGM battery without a second vehicle

Peak current: 1,000 A
Compatible batteries: 12 V lead-acid only (NOCO: not suitable for any other battery type)
Engine rating: Gas up to 6.0 L, diesel up to 3.0 L
Jump starts per charge: Up to 20 (NOCO figure)
Internal battery: 24 Wh lithium-ion
Protection: Spark-proof, reverse polarity; Manual Override for batteries below 2 V disables both
USB: USB-C in 5 V 2.1 A; out 5 V 2.1 A
Operating temperature: -4°F to 122°F (-20°C to 50°C)
Housing / weight: IP65, 2.45 lb
Warranty: 1-year limited

Small enough to keep in the frunk or glovebox, so it's in the car when the 12 V battery dies
Spark-proof clamps, and it won't fire if the clamps are reversed. It shows a red error light instead
Rated to operate down to -4°F, which matters because cold is when weak 12 V batteries give up

NOCO limits it to 12 V lead-acid batteries and says it is not suitable for any other type. Don't use it on a lithium 12 V battery unless the car's manual and NOCO both allow it
Manual Override switches off spark-proofing and reverse-polarity protection, so use it only as NOCO describes, for a lead-acid battery below 2 V
Charges the pack slowly at 2.1 A over USB-C. Top it up every few months so it's ready

Read the full write-up →

#3 · Jump pack — lists lithium compatibility

Battery Tender Jump N Start 1500 Amp Lithium Jump Starter (030-2020-WH)

Check price on Amazon(paid link)

A 1,500 peak amp lithium jump pack with smart clips. Battery Tender lists AGM, gel, lithium and standard lead-acid batteries as compatible, and it has a 12,000 mAh power bank.

Best for: A jump pack whose maker lists lithium 12 V batteries as compatible

Current: 750 A start / 1,500 A peak
Compatible batteries: AGM, GEL, Lithium, Standard (sealed or flooded lead-acid), per Battery Tender's product page
Engine rating: 12 V gas up to V8; diesel up to 5.5 L in Battery Tender's FAQ (its product description says 7.0 L)
Internal battery: 12,000 mAh lithium
Protection: Spark-proof smart clips, reverse polarity, short-circuit, over-current, over-temperature
Ports: USB-C in/out 5 V 3 A; QC 3.0 USB out; 12 V DC out (10 A)
Operating temperature: 32°F to 104°F (0°C to 40°C) per the manual
Certification: cETLus (UL 2743), UN38.3
Weight: 3.9 lb (pack only)
Warranty: 1-year limited

Unlike most jump packs, Battery Tender lists lithium alongside AGM, gel and flooded lead-acid as compatible battery types
The smart clips show green only on a good connection and sound an alarm if they're reversed, shorted or overheating
Larger 12,000 mAh pack, with USB-C and Quick Charge outputs that make it a useful power bank in an outage

The manual rates it to operate only from 32°F to 104°F, so it isn't rated for below-freezing use
"Lithium" on the compatibility list doesn't mean every automotive lithium low-voltage battery. Your car's manual still decides how, and where, to jump it
Battery Tender gives two diesel engine ratings (5.5 L and 7.0 L), so plan on the lower one

Read the full write-up →

#4 · Small-battery maintainer

Battery Tender Junior Multi-Chemistry 12V (022-0199-DL-WH)

Check price on Amazon(paid link)

A low-amp 12 V maintainer with a selector for lead-acid (flooded, AGM, gel, sealed) or four-cell LiFePO4 batteries from 3 to 30 Ah. It suits small starting batteries rather than car batteries.

Best for: Small 12 V starting batteries, such as a generator's, that sit between uses

Output: 12 V; 1 A per Battery Tender's current product page (some listings for this SKU say 800 mA)
Battery types: Six-cell lead-acid/AGM (flooded, AGM, GEL, sealed maintenance-free) or four-cell LiFePO4, selected by button
Capacity: 3 Ah to 30 Ah at 12 V
Dead batteries: Won't start below 3 V; LiFePO4 recovery mode for 4–8 V batteries (3-hour limit)
Protection: Spark-free clips, reverse polarity, short-circuit
Input: 120 V AC
Certification: ETL / cETL
Warranty: 5-year limited

Separate charge profiles for lead-acid and LiFePO4, so a lithium battery isn't left on a lead-acid float voltage
Includes ring terminals, so it can stay wired to a battery that only gets used in an outage
5-year warranty, longer than either jump pack here

Rated for 3–30 Ah only, which is too small for most car batteries. Check the battery's Ah rating before you buy
The lithium mode covers four-cell LiFePO4 only, not every lithium-ion low-voltage battery
Won't start on a battery below 3 V, so a fully flat lead-acid battery needs a different charger

Read the full write-up →

Working out what you need before you buy? Read the ev finance & ownership guides.