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Noco GB251 Boost Max User Manual

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Noco GB251 Boost Max User Manual

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Electrical Shock.
The product is an electrical device that can shock and cause serious injury. Do not cut power cords. Do not submerge in water or get wet.

Unmonitored, incompatible, or damaged batteries can explode if used with the product. Do not leave the product unattended while in use. Do not attempt to jump-start a damaged or frozen battery. Use products only with batteries of recommended voltage. Operate products in well-ventilated areas.

The product is an electrical device that emits heat and is capable of causing burns. Do not cover the product. Do not smoke or use any source of electrical spark or fire when operating the product. Keep product away from combustible materials.

Eye Injury.
Wear eye protection when operating the product. Batteries can explode and cause flying debris. Battery acid can cause eye and skin irritation. In the case of contamination of eyes or skin, flush the affected area with running clean water and contact poison control immediately.

Explosive Gases.
Working in the vicinity of lead acid is dangerous. Batteries generate explosive gases during normal battery operation. To reduce the risk of battery explosion, follow all safety information instructions and those published by the battery manufacturer and manufacturer of any equipment intended to be used in the vicinity of the battery. Review cautionary markings on these products and on the engine.

Important Safety Warnings

Proposition 65.
WARNING: This product can expose you to chemicals including lead and exhaust fumes, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to

Personal Precaution.
Only use the product as intended. Someone should be within range of your voice or close enough to come to your aid in case of emergency. Have a supply of clean water and soap nearby in the case of battery acid contamination. Wear complete eye protection and protective clothing while working near a battery. Always wash your hands after handling batteries and related materials. Do not handle or wear any metal objects when working with batteries including; tools, watches, or jewelry. If metal is dropped onto the battery, it may spark or create a short circuit resulting in electrical shock, fire, or explosion which may result in injury, death, or property damage.

Handle product with care. The product can become damaged if impacted. Do not use a damaged product, including, but not limited to, cracks to the casing or damaged cables. Do not use the product with a damaged power cord. Humidity and liquids may damage the product. Do not handle the product or any electrical components near any liquid. Store and operate products in dry locations. Do not operate the product if it becomes wet. If the product is already operating and becomes wet, disconnect it from the battery and discontinue use immediately. Do not disconnect the product by pulling on the cables.


Do not attempt to alter, modify or repair any part of the product. Disassembling a product may cause injury, death or damage to property. If a product becomes damaged, malfunctions, or comes in contact with any liquid, discontinue use, and contact NOCO. Any modifications to the product will void your warranty.

This product is only approved for use with NOCO accessories. NOCO is not responsible for user safety or damage when using accessories not approved by NOCO.

Prevent battery acid from coming in contact with the product. Do not operate the product in a closed-in area or an area with restricted ventilation. Do not set a battery on top of the product. Position cable leads to avoiding accidental damage by moving vehicle parts (including hoods and doors), moving engine parts (including fan blades, belts, and pulleys), or what could become a hazard that may cause injury or death.

The product is only compatible with 12-volt lead-acid batteries only. Do not attempt to use the product with any other type of battery. Jump-starting other battery chemistries may result in injury, death, or property damage. Do not jump-start a battery if you are unsure of the battery’s specific chemistry or voltage.

The Battery.

The built-in lithium-ion battery in the product should be replaced only by NOCO and must be recycled or disposed of separately from household waste. Do not attempt to replace the battery yourself and do not handle a damaged or leaking lithium-ion battery. Never dispose of batteries in household trash. Disposal of batteries in household trash is unlawful under state and federal environmental laws and regulations. Always take used batteries to your local battery recycling center. If the product battery is excessively hot, emitting an odor, deformed, cut, or is experiencing or demonstrating an abnormal occurrence, immediately stop all use and contact NOCO.

Battery Charging.

Charge the product with the included USB charge cable and a NOCO 10W 12V power adapter. A third-party USB cable and 5W or 10W power adapter that are compatible with USB 2.0 or power adapters compliant with one or more of the following standards EN 301489-34, IEC 62684, YD/T 1591-2009, CNS 15285, ITUL.2000. Be cautious of using low-quality power adaptors, as they may present a serious electrical risk that can result in injury to person, Device, and property.

If using a third-party USB power adapter, contact the manufacturer(s) to find out if your power adapter complies with the above standards. Using damaged cables or chargers, or charging when moisture is present, can result in electric shock. Using a generic or third-party power adapter may shorten the life of your product and cause the product to malfunction. NOCO is not responsible for the user’s safety when using accessories or supplies that are not approved by NOCO. When using a USB Power Adapter to charge the product, make sure that the AC plug is fully inserted into the adapter before you plug it into a power outlet.

Power adapters may become warm during normal use, and prolonged skin contact may cause bodily Important Safety Warnings EN injury. Always allow adequate ventilation around power adapters when using them. To ensure maximum battery life, avoid charging your product for more than a week at a time, as overcharging may shorten battery life. Over time, an unused product will discharge and must be recharged before use. Disconnect the product from power sources when not in use. Use the product only for their intended purposes.

How To Use

Charge the GB251
The GB251 comes partially charged out of the box and needs to be fully charged prior to use. Connect the GB251 using the included 12V DC car charger or XGC4 wall charger to the 12V IN port. The time to recharge a GB251 will differ based on the discharge level and the power source used. Actual results may vary due to battery conditions and the level of discharge.

Noco GB251 Boost Max User Manual fig 1

When recharging, the charge level of the internal battery is indicated by the Charge LEDs. The LEDs will slowly pulse ‘On’ and ‘Off’ and become solid until all four Charge LEDs are on. When the battery is fully charged, the Green 100% LED will be solid, and the 25%, 50%, and 75% Charge LEDs will turn “Off”. From time to time, the Green 100% LED will pulse indicating maintenance charging is occurring.

Connect to the Battery.

Carefully read and understand the vehicle owner’s manual on specific precautions and recommended methods for jump-starting the vehicle. Make sure to determine the voltage and chemistry of the battery by referring to your battery owner’s manual prior to using this product. The GB251 is for jump-starting 24-volt lead-acid battery systems only. Before connecting to the battery, verify that you have a 24-volt lead-acid battery system. The GB251 is not suitable for any other type of battery.

Identify the correct polarity of the battery terminals on the battery. The positive battery terminal is typically marked by these letters or symbols (POS, P,+). The negative battery terminal is typically marked by these letters or symbols (NEG, N,-). Do not make any connections to the carburetor, fuel lines, or thin, sheet metal parts. The below instructions are for a negative ground system (most common). If your vehicle is a positive ground system (very uncommon), consult the vehicle’s manual for proper jump-starting instructions. Connect the positive (red) battery clamp to the positive (POS, P,+) battery terminal and the negative (black) battery clamp to the negative (NEG, N,-) battery terminal or vehicle chassis.

Jump Starting.

  1. Make sure all of the vehicle’s power loads (headlights, radio, air conditioning, etc.) are turned off before attempting to jump-start the vehicle.
  2. Press the power button to begin to jump-start, and all LEDs will flash once. If you are properly connected to the battery, the white boost LED will illuminate and the battery charge LEDs will chase. A 60-second timeout countdown will begin as soon as a battery is detected.
  3. Try starting the vehicle. Most vehicles will immediately start. Some vehicles may require the GB251 to be connected for up to 30 seconds before starting. If the vehicle does not start right away, wait 20-30 seconds and try again. Do not attempt more than five (5) consecutive jump starts within a fifteen (15) minute period. Allow the GB251 to rest for fifteen (15) minutes before attempting to jump-start the vehicle again.
  4. Once you have started your vehicle, disconnect the battery clamps, and remove the GB251.

60-Second Timeout.
A 60-second countdown will be initiated as soon as a battery is detected. After 60 seconds have elapsed, the jump-starting function will be disabled. The boost LED will turn off and the internal battery charge LEDs will indicate the current charge level of the unit. To reset the jump-starting function, press the power button to power off the unit. Press the power button again to power on the unit and restart the jump-starting function.

Low Voltage Batteries & Manual Override.

The GB251 is designed to jump-start 24-volt lead-acid battery systems down to 3 volts. If your battery is below 3 volts, the boost LED will be “off”. This is an indication that the GB251 can not detect a battery. If you need to jump-start a battery below 3 volts there is a manual override feature, which allows you to force “on” the jump-start function. If the battery is below 3 volts, the boost LED will be off and the voltmeter will not display a voltage.

Powering Your USB & 12V Devices.
The GB251 has (2) USB-OUT ports and a 12V-OUT port (12V AUX/ cigarette lighter port). Plug in any standard USB device or 12V device (Up to 15A) and turn the GB251 “on” to start powering your devices.


Noco GB251 Boost Max User Manual fig 2


  1. Internal Battery Level Indicates the charge level of the internal battery.
  2. Error LED Illuminates red if reverse polarity is detected, or blinks “on” and “off” in various sequences (from 1 to 6 blinks) to convey error conditions.
  3. Hot LED Illuminates solid red; the unit is fully operational, but approaching the upper-temperature limit. Flashing red; the unit is too hot to jump-start, only the flashlight is available in this state.
  4. Cold LED Illuminates solid blue; the unit is fully operational, but approaching a lower temperature limit. Flashing blue; the unit is too cold to jump-start, only the flashlight is available in this state.
  5. Power Button Push to turn unit “on” & “off”.
  6. Power LED Illuminates white when the unit is “on”. Will illuminate orange after the 60-second timeout countdown until the clamps are removed from the Car Battery or the GB251 is power cycled ‘off’ and back ‘on’ again.
  7. Light Mode Button Toggles the ultra-bright LED light through 7 light modes: 100% > 50% > 10% > SOS > Blink > Strobe > Off
  8. Voltmeter/Countdown Timer. The built-in voltmeter reads the voltage of the vehicle’s battery for enhanced diagnostics and troubleshooting. The voltmeter will automatically read the voltage of any battery (or battery system) when the battery clamps are connected – even if the unit is powered off.
  9. Boost LED Illuminates white when boost is active. If the unit is connected properly to a battery, the GB251 will automatically detect a battery and go into boost mode (LED flashes white when the manual override feature is active).
  10. Manual Override Button To enable, push, and hold for three (3) seconds. WARNING: Disables safety protection and manually forces boost “on”. Only for use when a battery voltage is too low to be detected.


Error LED: Solid Red
Reverse polarity / Reverse the battery connections

Error LED: Blinking Red w/Cables Connected Properly
A short circuit was detected at the clamps. / Have the battery been checked by a professional?

Single (1) Flash
Short circuit detected on battery clamps. / Remove all loads, and reconnect clamps to battery.

Double (2) Flash
The high voltage detected at clamps (the GB251 is connected to a voltage system greater than 24V)

Quadruple (4) Flash
Charge timeout error (i.e. the GB251 has been in bulk charge for too long)

Quintuple (5) Flash
XGC OUT over current (i.e. more than 15amps is being drawn from the XGC OUT port)

Sextuple (6) Flash
BMS (Battery Management System) Fault. (Power GB251 “off” and “on” again to clear. If the problem persists contact Customer Support)

Hot LED: Solid
The unit is fully operational, but approaching the upper-temperature limit. / Allow the unit to cool.

Hot LED: Flashing
The unit is too hot to jump-start, only the flashlight is available in this state. / Allow the unit to cool.

Hot LED: Flashes Then All LEDs Of
The unit is too hot to jump-start or use other functions. / Allow the unit to cool, and bring the unit into a cooler environment.

Cold LED: Solid
The unit is fully operational, but approaching a lower temperature limit. / Allow the unit to warm up

Cold LED: Flashing
The unit is too cold to jump-start, only the flashlight is available in this state / Allow the unit to warm up.

Technical Specifications

  • Internal Battery: 137Wh Lithium Ion
  • 12V (Input): 12V/5A (14V Max)
  • Peak Current Rating: 3000A
  • 12V (Output): 12V, 15A Max
  • Operating Temperature: -20°C to +50°C
  • Housing Protection: IP65 (w/Ports Closed)
  • Charging Temperature: 0ºC to +40ºC
  • Cooling: Natural Convection
  • Storage Temperature: -20ºC to +50ºC (Avg Temp.)
  • Dimensions (L x W x H): 12.5 x 13.65 x 3.7 Inches
  • USB (Output): 5V, 2.1A
  • Weight: 13.65 Pounds


NOCO warrants that this product (the “Product”) will be free from defects in material and workmanship for a period of one (1) year from the date of purchase (the “Warranty Period”). For defects reported during the Warranty Period, NOCO will, at its discretion, and subject to NOCO’s technical support analysis, either repair or replace defective Products. Replacement parts and products will be new or serviceably used, comparable in function and performance to the original part, and warranted for the remainder of the original Warranty Period.

This Limited Warranty is made solely for the benefit of the original purchaser of the Product from NOCO or from a NOCO-approved reseller or distributor and is not assignable or transferable. To assert a warranty claim, the purchaser must: (1) request and obtain a return merchandise authorization (“RMA”) number and return location information (the “Return Location”) from NOCO Support by emailing or by calling 1.800.456.6626; and (2) send the Product, including RMA number, receipt or a warranty fee (fee required only if not providing receipt) of 45% of MSRP of the defective Product (the “Warranty Fee”) [RMA will include applicable Warranty Fee amount] to the Return Location.

NOCO One (1) Year Limited Warranty.

DO NOT SEND IN THE PRODUCT WITHOUT FIRST OBTAINING AN RMA FROM NOCO SUPPORT. THE ORIGINAL PURCHASER IS RESPONSIBLE (AND MUST PREPAY) FOR ALL PACKAGING AND TRANSPORTATION COSTS TO SHIP PRODUCTS FOR WARRANTY SERVICE. NOTWITHSTANDING THE ABOVE, THIS LIMITED WARRANTY IS VOID AND DOES NOT APPLY TO PRODUCTS THAT: (a) are misused, mishandled, subjected to abuse or careless handling, accident, improperly stored, or operated under conditions of extreme voltage, temperature, shock, or vibration beyond NOCO’s recommendations for safe and effective use; (b) improperly installed, operated or maintained;

(c) are/were modified without the express written consent of NOCO; (d) has been disassembled, altered or repaired by anyone other than NOCO; (e) the defects of which were reported after the Warranty Period. THIS LIMITED WARRANTY DOES NOT COVER: (1) normal wear and tear; (2) cosmetic damage that does not affect functionality; or (3) Products where the NOCO serial number is missing, altered, or defaced. You may register your NOCO product online at: no. co/register. If you have any questions regarding your warranty or product, contact NOCO Support (email and phone number above) or write to: The NOCO Company, at 30339 Diamond Parkway, #102, Glenwillow, OH 44139 USA.


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