4 amp car battery charger

The more discharged that your battery is, the longer it will take to recharge it. Batteries usually take several hours to recharge; if the battery is severely discharged (12.2 volts or less for an flooded battery) then it may take up to 12 hours or more to recharge. While recharging any battery, if the battery becomes hot when you touch it, stop charging it (a battery being charged should not get above 125 ferinheight). It is preferred to slow charge all batteries, slow charging rates vary depending on the battery’s type and capacity. When charging an automotive battery, 10-amps or less is considered a slow charge. Fast charging is NOT recommended, 20-amps or above is generally considered a fast charge. Repeated fast charging an automotive battery may overcharge the battery and reduce service life.

Step 1:
To determine how long it will take to recharge your battery, you must determine how much reserve capacity your battery has (refer to manufactures specs). In order to calculate the amount of amp-hours in a battery, the rule of thumb is to multiply the reserve capacity by 0.6. For example, if you have an automotive/flooded battery with 100 minutes reserve capacity, multiplied 100 by 0.6 = your battery would have approximately 60 amp-hours (at the 20-hour rate).

Step 2:
Use a voltmeter to measure the open circuit voltage of the battery (see chart below for state of charge). Open circuit voltage is the voltage of the battery with no load or disconnected from any circuit. Do NOT charge the battery before you test the open circuit voltage. If the voltmeter shows a voltage reading of 12.2 volts then the battery is approximately 50% charged. Since the battery is 50% charged, this means that there is approximately half of the 60 amp-hours in the battery or 30 amp-hours. Therefore it is necessary to put about 30 amp hours plus 20% more to compensate for the internal resistance in the battery for a total of 30 amps x 0.2 = 36 amp-hours to fully charge your battery.

Step 3:
If you charge your battery at a 10-amp rate and you need to replace 36 amp-hours in the battery. To determine how long (in hours) you will need to charge your battery, divided 36 by 10 = 3.6 or 3.6 hours to recharge your battery.

A 12 volt / 10 amp 3-stage automatic charger is the best charger for most automotive batteries. Unfortunately most chargers do not output the entire 10 amps during the charge cycle, because it automatically limits the voltage and the amperage during the charge cycle. You may actually only see about 1/2 the output over the time period that you are actually charging the battery. For that reason, it can easily take 12 hours or more to fully recharge the battery. Even after 12 hours, because of the reduced voltage, the battery may require more charging to get it 100% charged.

Step 4:
After the battery has cooled to room temperature use a voltmeter or check the cells with a hydrometer to determine the battery is fully charged.

The chart below is for quick reference, the method described above is the best way to determine how long it will take to charge your battery. The chart below shows how to determine the amount of time need to charge a battery based on the batteries CCA, open circuit voltage and charge rate. Batteries by Fisher does not recommend charging your battery above 10 amps.


You should always wear personal protection when charging and/or handling all batteries. The data and information contained herein are intended for use by persons possessing proper technical skill and knowledge, as they may deem appropriate and at their own risk. Batteries by Fisher, Inc. assume no liability whatsoever for results obtained or loss or damage incurred as a result of application of any data or information presented herein. Batteries by Fisher, Inc. believes the information contained herein is accurate as of its publication date. Information contained herein is subject to change without notice.

BUNDLE: Nitecore UM10 USB Li-ion Battery Charger For 18650/18490/18350/17670/17500/16340/14500/10440 w/ USB Wall & USB Car charger Plug and Lightjunction Keychain Light
Home Improvement (UM10)
  • USB Li-ion battery charger
  • USB input and Output
  • 1 Bay Charger
  • Displays battery power level
  • Includes: Charger, USB Wall Charger plug, USB Car charger plug, and keychain light
Universal Battery Charger, EASTSHINE S2 LCD Display Speedy Smart Charger for Rechargeable Batteries Ni-MH Ni-Cd AA AAA Li-ion LiFePO4 IMR 10440 14500 16340 18650 RCR123 26650
Speakers (EASTSHINE)
  • 1. Safety First: S2 Charger s Compliant Standard--UL cUL TUV GS PSE FCC CE C-TICKCB ROHS, and with Fire Retardant Materials, Intelligent Circuits and Worldwide Insurance.
  • 2. Universal Charger for: Ni-MH Ni-Cd A AA C SC Battery, Li-ion LiFePO4 IMR INR ICR 26650 25500 22650 18650 18490 18500 18350 17670 16340 RCR123A 14500 10440 Batteries.
  • 3. Speedy Charger for: Eneloop 2mAh AA 2-Hour, Amazonbasics 800mAh 0.8-Hour, 3400mAh Panasonic NCR18650B 3.5-Hour, 2500mAh LG HE2 2.5-Hour @ 1A Charge Current.
  • 4. Smart Charger: Automatically Detect battery Status, Select Charge Mode, Cut Off Power at Full or Overtime, and LCD Display Each Cell s Voltage and Type, Charging...
  • 5. What you get: S2 Smart Charger, Vehicles / Wall Adapter, Happy Card with 24 Hours Warm Service, 30 Days Free Refund, 2 Years Free Replacement, Lifetime Maintenance.
SYCEES Sycees 1000mA Fast USB Powered Battery Charger for 3.7V 18650 26650 Li-ion, 1.2V AA AAA Ni-MH Ni-Cd Rechargeable Battery and More
  • [ Ultra Fast Charging ] -- Up to 1mA charging current each slot (when 2A input), greatly shorten your waiting time. 3 LED shows you the charging status and charging...
  • [ Charging Everywhere ] -- Powered by any 5V USB power source such as solar panel, power bank, car adapter, computer, wall adapter, you could charge your batteries...
  • [ One Cover All ] -- Compatible with 3.7V Lithium-ion rechargeable batteries (size from 10340 to 26650) and 1.2V Ni-MH/Ni-Cd (A, AA, , , C) rechargeable batteries...
  • [ Mixed Charging ] -- Built-in micro processor automatically identifies battery types and selects appropriate charging voltage and current. Automatically detects...
  • [ Safe Charging ] -- Micro processor controls the charging process, automatically stops when fully charged. In addition, it s with reverse polarity protection and...
TAC10 GEAR TAC10 GEAR 2PCS 18650 4200mAh 3.7v Rechargeable Lithium Ion Batteries Plus AC/DC Digital Battery Charger - Charge From Home or Vehicle
Home Improvement (TAC10 GEAR)
  • (2) EXTENDED LIFE 18650 Rechargeable Lithium Ion Batteries Included
  • CHARGE FASTER with the Digital Charger you can charge your batteries in up to half the time of the standard TAC10 GEAR charger
  • STANDARD Wall outlet plug for convenient charging at home
  • CAR CHARGER adapter cord included so you can charger your li-ion batteries while on the go with any standard vehicle DC cigarette lighter port
  • EXCLUSIVE 1 YR TAC10 GEAR WARRANTY is only valid on purchases made from Triple M Futures. Unfortunately we are not able to offer a warranty or support for purchases...
UltraFire UltraFire A100 1000 Lumens Cree XM-L2 Tactical Zoomable LED Flashlight, Waterproof 5-Mode Torch Kit with Car Charger and 18650 Rechargeable Battery
Home Improvement (UltraFire)
  • 1) Emergency Flashlight kit with car charger and batteries, Prevent the sudden advent of accidents when you are traveling,Hiking,Camping!
  • 2) CREE XM-L2 LED,Lifespan:100, hours, up to 1lumens, Powerful enough to light up 180m distance objects.
  • 3) 5-Mode Arrangement: High / Middle / Low / Strobe / SOS.
  • 4) Battery Configuration: 1 x 18650 or 3x Batteries(not included) Input Voltage: 3.6-4.2V,4.2max
  • 5) Runtime: 3-5 hours Switch Type: Click/Clickie Switch Location: Tail-cap Lens: Convex Lens

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