Battery & electrical

Battery charger or trickle charger won't charge the battery

A charger that doesn't seem to be charging the battery is often due to a bad connection, a deeply discharged or dead battery, or a fault in the charger itself.

Difficulty
Easy
Time
1–8 hours (mostly waiting)
DIY cost
$0–$150
Pro cost
$100–$250

Symptoms

  • Charger indicator light shows an error or doesn't light up
  • Battery voltage doesn't rise after hours of charging
  • Charger clicks on and off repeatedly
  • Battery still won't start the car after a full charge cycle

Likely causes

  • CommonPoor connection between charger clamps and battery terminalsCorrosion or a loose clamp can prevent proper current flow even with a working charger.
  • CommonBattery too deeply discharged or sulfatedA battery left dead too long can become unable to accept a normal charge.
  • PossibleCharger set to the wrong mode or amperageSome chargers have settings for different battery types that need to match your battery.
  • PossibleFaulty chargerChargers can fail internally, especially older or budget models.
  • PossibleBattery is damaged or at end of lifeA battery with internal damage may not hold or accept a charge regardless of the charger.

What to do

  1. Clean the battery terminals of any corrosion before connecting the charger.
  2. Ensure the charger clamps are making firm, direct contact with the terminals (not just resting on corrosion).
  3. Check the charger's settings match your battery type (standard, AGM, etc.) if it has selectable modes.
  4. Let the charger run for the recommended time (often several hours) before checking progress, since deeply discharged batteries charge slowly at first.
  5. Test the battery voltage with a multimeter before and after charging to see if there's any change at all.
  6. Try the charger on a different, known-good battery to rule out a faulty charger.
  7. If the battery won't accept any charge after an extended attempt, it's likely too far gone and needs replacement.
  8. Have the battery load-tested at an auto parts store to confirm whether it can be saved.

Tools and parts

  • Battery charger or trickle charger
  • Multimeter
  • Wire brush for terminal cleaning
Replacement 12V batterySearch: “car battery for [your car make model year]”

When to call a pro

If a battery won't take a charge after a full attempt and terminals are clean, it likely needs replacing rather than more charging time.

Safety

Use caution

Charge batteries in a ventilated area away from open flames or sparks, since they can vent small amounts of flammable gas while charging.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.