How to test an off grid battery bank
Desulphators such as The Battery Life Saver™ electronic device or equalizing a battery bank will not help a battery or batteries that have an open or shorted cell. In order to tell if a battery as an open or shorted cell, simply perform the following tests. You will need a voltmeter and a hydrometer to perform both of these tests.
IMPORTANT: Please review our Safety Precautions before handling or testing any battery!
Safety First! Wear protective clothing, goggles and gloves when handling batteries.
Step 1: Physical & Mechanical Inspection
A mechanical inspection is really important as it can save you from future battery trouble. Replace cracked or broken batteries, clean or replace rusted or broken connections. On flooded/wet batteries check the water levels. The water level should be high enough to just cover the plates. Use only distilled water and do not overwater as it can spill and electrolyte is corrosive.
Step 2: Preparing the Tests
a.) Make sure you turn off any instruments or accessories that will drain the battery or battery system during testing.
b.) Charge the battery or battery system until it is fully charged .
c.) If the system has multiple batteries connected, we recommend to disconnect them from each other to get accurate readings. Let the batteries sit for 4 to 12 hours, the longer the better. This important because if you measure the voltage immediately after charging, you will not be measuring the true voltage of the battery.
Step 3: Testing for a Short Cell
a.) With a voltmeter, measure the voltage of each individual battery.
b.) Reference the chart below to determine if a battery has a shorted cell.
Battery Voltage Reading of a Short Cell
6 volt 4.3 volts
8 volt 6.5 volts
12 volts 10.6 volts
Example: If a 6 volt battery is reading below 4.3 volts it has a short cell .
Step 4: Testing for an Open Cell in a Flooded/Wet cell battery
If you have the sealed type batteries, this test method cannot be used.
Use a temperature compensating battery hydrometer for this test.
a.) With the hydrometer, measure and record the specific gravity of each battery cell. ( Example: Battery #1— Cell 1= 1.250, Cell 2=1.275, Cell 3= 1.275). Fill & drain the hydrometer a few times before pulling a sample.
b.) Compare the specific gravity readings between each battery. If a battery has a difference of more than .05 between the cells, that battery has an open cell.
Example readings:
Three 6 volt batteries
Cell #1 Cell #2 Cell #3 Condition
Battery A 1.250 1.225 1.250 Recoverable
Battery B 1.275 1.250 1.225 Recoverable
Battery C 1.200 1.250 1.275 Open Cell
Battery C has an Open Cell because the difference between Cell #1 and Cell #3 is .075, more than .05.
Any battery that has a Short or Open Cell needs to be replaced. If the difference in SG between any two cells is greater than 0.025, the battery bank needs to be equalized to ensure that all cells receive a full charge.