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How to Test a Battery: LiFePO4 Guide
Posted by author 1st Mar., 2023
Test a battery │ Leisure battery │ LiFePO4 │ Lithium ion battery │ Multimeter
Total Words: 1743, requires 4 minutes 15 seconds
Testing a battery can be easy.
You will need two gauges to test a LiFePO4 battery: a multimeter to test the voltage under the direct current(DC) area, or a battery tester to test the capacity or voltage from your input data.
Is that really important to test a battery?
Why do we test a battery by voltage not current?
How to test a LiFePO4 battery?
What can we know from the testing result?
Let’s check it out.
Is It Important to Test a Battery?
No battery can last forever.
Whether they are the lead acid battery, the LiFePO4 battery, the Pansonic battery, the blade battery, or the the 4680 battery, they all have limited lifespan – due to their failure of material construction and the increasing internal resistance.
Battery is almost the most expensive part of the whole system/vehicle and it degrades after three to five years’ working from its capacity and running time.
We need to check the battery before it is too late to repair or replace.
It might be a battery cell falloff in an integrated system, or even the whole battery pack in an energy storage system.
That doesn’t mean you got a ungraded battery with worse battery management system(BMS) or poor conformity lithium ion battery, but goes in correlation with the environmental temperature, frequent over-charge and over-discharge condition, and the electrolyte and electrode material choosing for the battery as well.
One of the battery maintenance is battery testing. It is the best way to know the battery’s condition and to diagnose obvious causes of some battery failures.
When you have to know whether the battery is under over discharge situation, or is too weak to hold a charge, you will need a multimeter or a battery tester.
The Battery Testing Principle
Why can we test the battery condition through multimeter or battery tester? The answer is the voltage*.
*You can skip to next part to learn about how to test a battery.
Since the Redox Reaction inside the battery becomes weaken and weaken through every discharging, which also brings about the electric potential variation such as activation polarization, ohmic polarization and concentration polarization, the maximum voltage will decrease slightly as well through years along with the deceasing capacity.
See picture below.
While the minimum voltage and the voltage in between remains the same(within 3000 cycles).
According to the Ohm Law of the whole circuit: “E=I(R+r)”, when external circuit remains the same resistance “R”, the voltage inside the battery “Ir=E-U” gets larger, the voltage in external circuit(terminal voltage) “U=IR=E-Ir” will get less, which brings down the battery voltage with time goes by.
That comes to the conclusion: When your battery fades down, it will directly tell you in voltage*.
*A bad battery with current testing by multimeter can be mistaken for a good battery since multimeters have very high input impedance(>1 Mohm), which only require very little current(<12 uAmps).
Now let’s move on to see how to test a LiFePO4 battery.
How to Test a Battery?
1. Testing by Multimeter
Even there are many other gauges to measure and test the batteries, multimeter* is still the most cheaper, safer, quicker and easier device to use.
*We only talk about digital multimeter here rather than voltmeter or analog multimeter.
So how to test a battery with a multimeter?
Step 1: Clean the terminal
First you need a ready-to-test battery. It doesn’t have to be remove from the system or vehicle, but you need to know where the terminal or the binding post is.
Make sure that there is no dirt or corrosive on the terminal, which is also known as negative terminal with “-” or “minus” or black cover and positive terminal with “+” or “plus” or red cover on the battery.
A sandpaper* can clean both dirt and corrosive terminal layer. A little spot is quite enough for the testing, so you don’t need to push too hard.
*Just remove the circuit of the system from the terminal if you don’t have any sandpaper either.
Step 2: Set the multimeter
Usually you can see four blocks on the multimeter: the display area, the button area,the knob area, and the connection area.
- ①Connect the plug of the red probe to the VΩmA port, and the plug of the black probe to the COM port on the connection area.
- ②Turn to the “V-” or “V⎓” or just “V” on the knob area, which mean you are using DC current*(direct current). Put the knob on the proper voltage measuring range, mostly 20V or 200V**.
*“V⎓” means DC current(direct current) while “V~” means AC current(alternating current). If “V” is the only voltage option you can see on your multimeter, that’s the exact DC current we need.
**You can turn to the max voltage range if you don’t know how large it is, but please turn back down gradually until you can see a much more precise data from the multimeter. The battery that we use is usually 12V, 48V or 96V. So 200V could be the proper range to measure.
Step 3: Connect to the battery
It is better to wear a glove before you test the battery*. Connect red probe of the multimeter to the positive terminal of the battery, connect black probe of the multimeter to the negative terminal of the battery**.
*Human body’s safety voltage is 36V, and 24V is the most safe and consecutive voltage that human can reach to(for current under 10mA). There are some batteries go to between 48V and 92V, even though the battery is designed to be safe without shocking you, please don’t touch both terminals by hands at the same time, whether the battery is turning on or turning off at the moment.
**The pointer of the multimeter will go the other way if connect the wrong side, but the data is still referable within slightly differences – because you are testing the negative pole data rather than positive pole.
Now read the data on the display area.
2. Testing by Battery Tester
More accurate parameters with charging test(current, state of charge, used cycles), soh test(rest capacity, voltage, remaining discharging hours) is giving by a battery tester.
Battery tester is designed to test the rest of the capacity from battery’s charge. They work by applying a load and monitoring the voltage response.
When using the battery tester, it has to be a lithium ion battery tester to be exact. And here we just talk about lifepo4 battery tester(hand-held electronic battery hold tester)*.
*It is always recommended to refer to the instruction manual or guideline for your particular model. It also tells whether a disconnection of the battery from the system/vehicle is necessary or not – mostly don’t.
A good lithium ion battery tester can tell you battery’s operating voltage, internal voltage, internal resistance, capacity, self discharge rate, performance condition, safety condition, sealing condition, and how you have used the battery through data(over-charge, over-discharge, etc)
So how to test a lithium ion battery by a battery tester?
Step 1: Open the power switch.
Step 2: Input the data.
Set up the capacity and voltage information with ▲/▼ on the battery tester. It should be the exact parameter from your battery specification, such as 12V of voltage and 100Ah of capacity.*
*Most battery testers will record the data you have inputted before, just don’t use onto other batteries without resetting. If you are not checking with LiFePO4 battery testers, please also select “battery type” by LiFePO4 or “cell voltage” by 3.2V.
Step 3: Connect to the battery.
Connect red clamps/leads to the positive(+) terminal of the battery and the black clamps/leads to the negative(-) one*. Once you hear a tone like “BI” or it turns green from the tester, that means a correct connection.
*Please noted that do not connect the red clamps/leads to the negative terminal or black clamps/leads to the positive. Do not use a battery tester to test a dead battery as well. These will cause a short circuit.
Step 4: Choose what you need.
Choose the capacity testing, current testing or voltage testing button on the battery tester, press “Test” or “OK” for testing.
Still easy enough.
What’s the result?
What can we know after we test the battery?
A LiFePO4 battery cell has the voltage between 2.50V ~ 3.65V, recommended working voltage between 2.70V ~ 3.80V and a dead battery is usually with voltage under 2.30V which maintains no further charging – you can fully charge a over-discharge battery without problem.
See the listed voltage below for reference.
|LiFePO4||Working Voltage||10.0V ~ 14.6V||20.0V ~ 29.2V||40.0V ~ 58.4V||50.0V ~ 73.0V||75.0V ~ 109.5V|
|Charging Voltage||14.6V ~ 15.2V||29.2V ~ 30.4V||58.4V ~ 60.8V||73.0V ~ 76.0V||109.5V ~ 114.0V|
|LiNiCoMnO2||Working Voltage||8.25V ~ 12.6V||19.25V ~ 29.4V||35.75V ~ 54.6V||44.0V ~ 67.2V||68.75V ~ 105V|
|Charging Voltage||12.6V ~ 12.9V||29.4V ~ 30.1V||54.6V ~ 55.9V||67.2V ~ 68.8V||105.0V ~ 107.5V|
When you can’t charge a under-voltage battery, it is time to replace the battery.
That doesn’t make a rechargeable lithium ion battery a good battery as well. When a fully charged battery drops voltage much quicker than it used to be, it needs to be repaired by your manufacturers or retail stores – Some battery cells inside are inactive or BMS could be malfunctioning already.
Whichever happens after you are testing the battery, whether it needs to be repaired or replaced, there are three ways to go:
- 1.Re-test the battery after half or fully charging the battery, it is better to be two to three hours later after your first battery test.
- 2.A low voltage but high current battery is always the sign to replace your battery. It is kind of a dead battery on your
- 3.A high voltage that drops fast is an impaired battery, it needs to be repaired and most parts inside are still good enough for next hundred trips.
You don’t need to be any professor or specialist on the battery, leave it and trust your manufacturer and supplier – A simple test is all you need to do.
The battery’s voltage reduces over time as the battery loses its lithium-ion, and it reaches a point where you cannot use the battery for an extended period.
Testing your battery is not only a significant method to know how the battery was, but also an improving progress to learn about how to use the battery in the future. And most importantly, testing a lithium ion battery is not that hard to be done, is it?
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