The most capable unit in the Charge N Start lineup. The Battery Tender® Charge N Start 4120 combines a 4 Amp ISM smart battery charger with 1200 Amps of portable lithium jump starting power — four times the charging output of the CNS 1100 and 1120, same 1200 Amp jump starting power as the CNS 1120. Faster battery recovery for larger vehicles. Maximum jump starting power. The complete battery charger and jump starter solution in one portable unit.

Two Devices. Maximum Output. One Unit.

As a 4 Amp ISM smart battery charger and maintainer, it recovers and maintains larger automotive batteries significantly faster than 1 Amp alternatives. As a 1200 Amp portable lithium jump starter, it starts full-size vehicles with gas engines up to 6.0L and diesel engines up to 4.0L without jumper cables or a second vehicle.

How to Jump Start a Car — 1200 Amps Without Jumper Cables

Jump starting a dead car battery with the CNS 4120:

Connect the red jump start clamp to the positive (+) terminal on the dead battery
Connect the black jump start clamp to a ground point or the negative (−) terminal
Spark-proof technology confirms connection — reverse polarity protection prevents damage from incorrect connections
Crank for up to 5 seconds per attempt with 30 seconds between attempts
Once running, disconnect and store

No second vehicle. No cable management. 1200 Amps handles the full range of passenger cars, trucks, and SUVs with gas engines up to 6.0L and diesel engines up to 4.0L.

How to Jump Start a Motorcycle, ATV, or Powersports Vehicle

The CNS 4120's 1200 Amp lithium jump pack is among the most powerful portable motorcycle and powersports jump starters available — more than sufficient for any 12V powersports battery:

Access the battery — remove the seat or open the battery compartment
Connect the red jump start clamp to the positive (+) terminal
Connect the black clamp to a clean frame ground point or the negative (−) terminal
Crank for no more than 3–5 seconds — small powersports batteries respond immediately to lithium jump pack power
Once running, disconnect and secure the compartment

The CNS 4120's 4 Amp ISM charger is particularly well-suited for powersports applications where the battery is used infrequently and benefits from faster recovery after seasonal storage. Motorcycles, ATVs, UTVs, side-by-sides, personal watercraft, and snowmobiles stored for weeks or months are among the highest-risk dead battery scenarios — ISM maintenance charging at 4 Amps keeps them at full capacity and reduces the need for the jump start function over time.

How to Jump Start a Truck or Large SUV

For full-size trucks, diesel pickups, and large SUVs with high-capacity batteries, the 4 Amp charger recovers depleted batteries more than three times faster than 1 Amp alternatives, and 1200 Amps provides ample cranking power for cold starts and marginally charged batteries:

Locate the battery — typically under the hood, occasionally in the truck bed or under the seat
Connect red clamp to positive (+), black clamp to ground or negative (−)
Spark-proof confirmation before current flows
Crank for up to 5 seconds with 30-second intervals between attempts
Disconnect once running

CNS 4120 vs CNS 1120 — Why 4 Amp Charging Matters

Both units deliver 1200 Amps of jump starting power. The CNS 4120's 4 Amp charger recovers large automotive batteries more than three times faster during bulk charge — meaningful for trucks, SUVs, RVs, and boats where 1 Amp recovery takes significantly longer.

Two Separate Clamp Sets — Not Interchangeable

Dedicated charging clamps for ISM maintenance. Dedicated jump start clamps for 1200 Amp cranking. Not interchangeable — engineered for their specific functions.

Internal Lithium Jump Pack — Auto-Switch Keeps It Ready

The Charge N Start 4120 automatically switches between charging the external vehicle battery and topping up the internal jump pack when it detects the internal level has dropped — ensuring 1200 Amps of jump starting power is always available when needed.

The Prevention and the Cure — At Full Output

4 Amp ISM prevents sulfation across all battery sizes. 1200 Amp jump pack handles unexpected failures. One unit, both outcomes, maximum output.

Multi-Chemistry Charging: Lead-Acid and Lithium

The 4 Amp smart charger supports both lead-acid and Lithium (LiFePO4) battery chemistries with a manual selector delivering the correct ISM charging profile for each type. Compatible battery size range: 14Ah to 100Ah at 12V. Lead-acid: flooded, AGM, gel cell, sealed MF. Lithium: LiFePO4.

ISM: 4-Stage Smart Charging at 4 Amps

Initialization — Battery health check and polarity confirmation before charging begins
Bulk Charge — Full 4 Amp output restores depleted capacity efficiently
Absorption — Current tapers automatically as the battery approaches full charge, preventing overcharge damage
Float Maintenance — Correct maintenance protocol for the selected chemistry delivered 24/7, indefinitely

Compatible Vehicles

Passenger cars and trucks up to 6.0L gas / 4.0L diesel
Motorcycles and touring bikes
ATVs, UTVs, and off-road vehicles
Boats and marine vessels
RVs and campers
Any 12V lead-acid or Lithium battery from 14Ah to 100Ah

Why Lithium Outperforms Lead-Acid Jump Boxes

Consistent peak Amps in cold weather when lead-acid units lose capacity most. Months of charge retention in storage. Fraction of the weight of lead-acid units. Stays ready through continuous wall-connected maintenance charging without degradation.

Safety Features

Spark-proof connection on both clamp sets — no current flows until connection is confirmed correct
Reverse polarity protection on both clamp sets
Short-circuit protection
Overcurrent protection
ETL and CETL certified

1-Year Limited Warranty | DeLand, Florida Since 1965

EV 12V Jump Starters

Price

Collections

Jump N Start 1500 Amp Lithium Jump Starter

Jump N Start 800 Amp Jump Starter and Tire Inflator

Jump N Start 600 Amp Lithium Jump Starter

Charge N Start 4120 — 4 Amp Battery Charger & 1200 Amp Jump Starter