Testing is required to determine the ability of a battery to function properly. The accuracy of the testing changes with temperature, specific gravity, age of the battery, type of battery, etc. An accurate test has more than one step.
Step l: Visual inspection
Step 2: Specific gravity check (hydrometer)
Step 3: 421 test *
Step 4: "Load test"
Cautions: Wear safety glasses. DO NOT break live circuits at battery terminals. When testing, be certain to remove gases at battery cover caused by charging.
*"421" and Load Test equipment is available from many automotive test equipment suppliers.
Warning: The information on
this page should not be used for "Maintenance free",
"Gel" and/or "AGM" type batteries. Also, these type
batteries are not always charged properly by an old fashion battery charger.
Visual Inspection: Check for obvious damage, such as a cracked or broken case that shows loss of electrolyte. Check around the top of the case around the posts as well.
A. Obvious damage?
B. No obvious damage ?
* Check electrolyte level
Below top of plates in one or more cells, Add water to
just above separators but not to split ring
Charge for 15 minutes @ 15-25 amps with non-flame
arrestor vent caps removed but leave flame arrestor
caps in place.
(See tips on charging here.)
* Electrolyte level above top of plates in all cells?
Proceed to Step 2
Note: Before performing any tests on
a battery, check electrolyte level and top off with only distilled water, as
needed. The likelihood of a battery explosion increases significantly as the
temperature and charging rate increases and the electrolyte level decreases.
Replace battery if any signs that the battery has run completely dry, cracks in
battery case, and/or terminal post damage.
Specific Gravity (Hydrometer) Test
A. 50 points or more variation between highest and lowest cell?
* Replace battery
B. Less than 50 points variation between highest and lowest cell
* Specific gravity 1.100 @ 80o or more in all cells?
If "421" tester is available, go to Step 3.
If not available, go to Step 4.
(6 and 8 volt. proceed to Step 4)
* Specific gravity less then 1.100 in one or more cells?
Proceed to Step 4
Connect 300 amp load for 15 seconds (421" test)
* Meter reading "bad'?
* Meter reading "good" No history of trouble?
Fully charge, clean, add water to split ring
and return battery to service .
* History of trouble?
Proceed to Step 4
Charge battery, if necessary, until all cells are at least
1.200 specific gravity. Remove all vent caps.
* If unable to obtain specific gravity of 1.200 @ 80o in all cells?
* Specific gravity of 1.200 or more @ 80o in all cells?
Connect 300 amp load for 15 seconds
* "Smoke" in one or more cells?
* "No smoke"?
1. Place thermometer in one cell.
2. Apply load equal to 3 times the ampere-hour rating of the battery
(2 times for 6-volt batteries)
3. Read voltage at 15 seconds with load connected,
4. Remove load and read electrolyte temperature, then compare
voltage and temperature readings with Chart below.
* Less than voltage on chart?
* Same as or greater than voltage on chart?
Fully charge, clean, add water to split
ring and return battery to service.
BATTERY VOLTAGE and TEMPERATURE CHART (Fahrenheit)
Note: Voltage must not drop below minimum listed at given
temperature when battery is subjected to the proper
load for 15 seconds and is 1.200 specific
gravity @ 80o or more.