Battery State of Charge

Maintenance-Free Batteries

Read the battery open circuit terminal voltage with a digital voltmeter such as Rotunda Digital Volt-Ohmmeter 007-00001 or equivalent, capable of reading 1/100 of a volt. If open circuit voltage of battery is below 12.4 volts and the battery has passed the capacity test, charge the battery.

Low-Maintenance Batteries

Use a hydrometer such as Rotunda Battery and Anti-Freeze Tester 021-00046 or equivalent to check the specific gravities of all cells.

In order to obtain an accurate specific gravity reading, it must be corrected to the standard temperature of 26°C (78°F). The correction factor of four points (0.004) is used for each 6°C (10°F) change in temperature. Four points (0.004) are added to the indicated reading for each 6°C (10°F) increment above 26°C (78°F) and four points (0.004) are subtracted for each 6°C (10°F) increment below 26°C (78°F).

If the difference between cells is 50 points (0.050) or more, the battery is not satisfactory for service and should be replaced.

If the difference between cells is less than 50 points (0.050) and one or more cells are less than 1.225, charge the battery for 20 minutes at 35 amps and conduct the capacity test. If the battery fails, replace the battery. If it passes, add water if necessary and charge the battery.

If the difference between cells is less than 50 points (0.050) and all cells are above 1.225, conduct the capacity test. If the battery fails, replace the battery. If it passes, return to service.  

BATTERY TESTING PROCEDURE — TEST A

A1 VISUAL INSPECTION

• Remove negative cable, then positive cable.

• Check for dirty or corroded connections.

• Are connections OK?

CLEAN terminals and clamps. GO to A2 .

Yes
GO to A2 .

 

A2 LOOSE BATTERY POST

• Check for loose battery posts.

• Are posts OK?

No
REPLACE battery.

Yes
GO to A3 .

 

A3 CRACKED BATTERY COVER

• Remove holddowns and shields.

• Check for broken/cracked case or cover.

• Is cover OK?

No
REPLACE battery.

Yes
GO to A4 .

 

A4 BATTERY CAPACITY AND LOAD TEST

NOTE: Whenever possible, test and charge battery at or near room temperature.

• Use a high rate discharge tester with a variable rate control or a fused rate tester with meter compensation for different battery electrical sizes. Follow instructions supplied with tester for the battery capacity test.

• Recommended discharge rate at 27°C (80°F): one-half of the cold cranking amps.
  
  

  Cold Cranking Amps	Discharge Rate Amps
  540	270
  460	230

  
  

• Voltage readings at 15 seconds for good battery (Battery Capacity Test).
  
  

  Approximate Battery Temperature	Minimum Load Voltage
  27°C (80°F) and above	9.6
  21°C (70°F)	9.6
  16°C (60°F)	9.5
  10°C (50°F)	9.4
  4°C (40°F)	9.3
  -1°C (30°F)	9.1
  -7°C (20°F)	8.9
  -12°C (10°F)	8.7
  -18°C (0°F)	8.5

  
  

• Wait 2 minutes and check the Open Circuit Voltage (OCV).

• Measure OCV with a digital voltmeter capable of reading 1/100 volt.

Passed the minimum load voltage and OCV above 12.40
Battery OK.

Passed the minimum load voltage and OCV below 12.40
Battery OK but needs charging.

Failed the minimum load voltage and OCV above 12.40
Battery worn out. REPLACE battery.

Failed the minimum load voltage and OCV below 12.40
CHARGE battery for 20 minutes at 35 amps. REPEAT Step A4 (load test).

   

Passed the minimum load voltage. Battery OK but needs charging.

   

Failed the minimum load voltage. REPLACE battery.

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