Testing Procedures For Lead Acid Batteries

Battery Testing Procedures From Manbat

Preparation
Remember the phrase ‘safety first’ so always wear goggles, rubber gloves, and a rubber apron and ensure that the maintenance carried out in a well-ventilated area. Always follow the correct handling protocols when lifting or moving batteries. So keep a straight back and if in any doubt seek assistance from a colleague. Never smoke or use a naked flame when around batteries.
Inspection
Examine the outside of the battery, looking for cracks in the case and ensure that the posts and connections are free of dirt, fluids and corrosion. Any fluids on or near to the battery could indicate that the electrolyte is spilling or leaking out of the battery. Spilt electrolyte can cause serious damage.
Open Circuit Voltage Testing
For accurate voltage readings batteries must have been idle for at least 6 hours prior to testing.
Disconnect all loads from the battery and measure the voltage with a DC voltmeter. Consult the table below for the state of charge and charge the battery if it is 80% or less of full capacity.

STATE OF CHARGE % ...............SPECIFIC GRAVITY............... 12v BATTERY
........100...................................................1280 .....................................12.73
..........90 ..................................................1258 .....................................12.62
..........80 ..................................................1238......................................12.50
..........70...................................................1217.......................................12.37
..........60...................................................1195.......................................12.24
..........50...................................................1172.......................................12.10
..........40...................................................1150......................................11.96
..........30..................................................1124.......................................11.81
.........20...................................................1100.......................................11.66
.........10...................................................1073........................................11.51

Specific Gravity Testing
Do not add water to the cells prior to testing.
Fill and drain the hydrometer three or four times prior to testing and then ensure that you have enough sample electrolyte in the hydrometer to completely support the float, keep the pipe submerged in the electrolyte.
Take a reading, and return the electrolyte to each cell after testing. The readings should be between 1270 to 1280. If any of the cells read below 1240, then put the battery on a complete charge, and retake the specific gravity readings again afterwards. Should the cells still read low then perform an equalising charge (detailed below).
If any of the cells still read low after performing the complete charge and a subsequent equalising charge, then the battery is likely be reaching the end of its life and should be replaced.
Watering
Prior to charging, there should be enough electrolyte to cover the plates. If the battery has been discharged (partly or fully), the liquid level should also be above the plates. If necessary, top up the cells before charging with distilled or deionised water to cover the plates. A thorough charge will ensure the water is fully absorbed into the electrolyte.
Charging
The key to charging batteries requires administering the correct amount of current at the right voltage. The vast majority of charging equipment automatically regulates these values, however some chargers do allow the user to set these values. A non-automatic charger should be set at 10% of the Ah (Amp/Hour) capacity of the battery. E.G. 10amps for a 100 Amp/Hour battery.
For further information concerning any area of battery care visit: www.manbat.co.uk