Yamaha YZF-R125 Service Manual: Checking and charging the battery


Batteries generate explosive hydrogen gas and contain electrolyte which is made of poisonous and highly caustic sulfuric acid.

Therefore, always follow these preventive measures:

  • Wear protective eye gear when handling or working near batteries.
  • Charge batteries in a well-ventilated area.
  • Keep batteries away from fire, sparks or open flames (e.g., welding equipment, lighted cigarettes).
  • DO NOT SMOKE when charging or handling batteries.
  • Avoid bodily contact with electrolyte as it can cause severe burns or permanent eye injury.


  • Skin - Wash with water.
  • Eyes - Flush with water for 15 minutes and get immediate medical attention.


  • Drink large quantities of water or milk followed with milk of magnesia, beaten egg or vegetable oil. Get immediate medical attention.

1. Remove:

  • Rider seat Refer to "GENERAL CHASSIS" on page 4-1.

2. Disconnect:

  • Battery leads (from the battery terminals)

First, disconnect the negative battery lead "1", then the positive battery lead "2".

Checking and charging the battery

3. Remove:

  • Battery

4. Check:

  • Electrolyte level The electrolyte level should be between the minimum level mark "a" and the maximum level mark "b".

    Below the minimum level mark Add
    distilled water to the proper level.


Add only distilled water. Tap water contains minerals which are harmful to the battery.

5. Check:

  • Specific gravity Less than 1.280 Recharge the

6. Charge:

  • Battery

Battery charging amperage and time 5.5 amps/10 hrs


Do not quick charge a battery.

  • Loosen the battery sealing caps.
  • Make sure the battery breather hose and battery vent are free of obstructions.
  • To ensure maximum performance, always charge a new battery before using it.
  • Do not use a high-rate battery charger.

    They force a high-amperage current into the battery quickly and can cause battery overheating and battery plate damage.

  • If it is impossible to regulate the charging current on the battery charger, be careful not to overcharge the battery.
  • When charging a battery, be sure to remove it from the vehicle. (If charging has to be done with the battery mounted on the vehicle, disconnect the negative lead from the battery terminal.)
  • To reduce the chance of sparks, do not plug in the battery charger until the battery charger leads are connected to the battery.
  • Before removing the battery charger lead clips from the battery terminals, be sure to turn off the battery charger.
  • Make sure the battery charger lead clips are in full contact with the battery terminal and that they are not shorted. A corroded battery charger lead clip may generate heat in the contact area and a weak clip spring may cause sparks.
  • If the battery becomes hot to the touch at any time during the charging process, disconnect the battery charger and let the battery cool before reconnecting it. Hot batteries can explode!


  • Replace the battery whenever:
  • battery voltage does not rise to specification or bubbles fail to rise during charging,
  • sulphation of one or more battery cells occurs (as indicated by the battery plates turning white or material accumulating in the bottom of the battery cell),
  • specific gravity readings after a long, slow charge indicate that one battery cell's charge is lower than the rest,
  • warpage or buckling of the battery plates or insulators is evident.

7. Check:

Battery breather hose and battery vent Obstruction → Clean.

Damage → Replace.

8. Install:

  • Battery

9. Connect:

  • Battery breather hose "1"

Checking and charging the battery

  • When checking the battery, make sure the battery breather hose is properly installed and routed correctly. If the battery breather hose is positioned so as to allow electrolyte or hydrogen gas from the battery to contact the frame, the vehicle and its finish may be damaged.
  • Make sure the battery breather hose is properly routed away from the drive chain and from below the swingarm.


  • Battery terminals Dirt → Clean with a wire brush.

    Loose connection → Connect properly.


  • Battery leads (to the battery terminals)

First, connect the positive battery lead "1", then the negative battery lead "2".

Checking and charging the battery


  • Battery terminals


  • Rider seat Refer to "GENERAL CHASSIS" on page 4-1.
    Checking the fuses
    The following procedure applies to all of the fuses. CAUTION:To avoid a short circuit, always turn the main switch to "OFF" when checking or replacing a fuse. 1. Remove: Ri ...

    Checking the relays
    Check each switch for continuity with the pocket tester. If the continuity reading is incorrect, replace the relay. 1. Disconnect the relay from the wire harness. 2. Connect the pocket tester ( ...

    Other materials:

    Vehicle identification number The vehicle identification number "1" is stamped into the right side of the steering head pipe. Model label The model label "1" is affixed to the frame. This information will be needed to order spare parts. ...

    Installing the piston and cylinder
    1. Install: Top ring "1" 2nd ring "2" Oil ring expander "3" Lower oil ring rail "4" Upper oil ring rail "5" NOTE: Be sure to install the piston rings so that the manufacturer marks or numbers face up. 2. Install: Piston "1" Piston pin "2" Piston pin clips "3" NOTE: ...

    Installing the front brake master cylinder
    1. Install: Brake master cylinder "1" Brake master cylinder holder "2" NOTE: Install the brake master cylinder holder with the arrow mark "a" pointing forward. Align the end of the brake master cylinder holder with the punch mark "b" on the handlebar. First, tighten the front bo ...

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