How To

How to Test a Battery with a Multimeter?

The question is asked again and again in the vastness of the Internet I have so far found no quick answer. So here’s my attempt to answer the following questions:

  • My battery is no longer charging – is it defective?
  • How can I check for myself if my body battery in the camper is broken?
  • The battery lasts only 3 hours; then the light goes out – defective?
  • Can I have a battery tested at ATU?

When is a lead battery defective?

A lead battery is generally considered to be defective if it can no longer deliver power and the remaining capacity has dropped to zero. In typical operation, a faulty battery can usually only be recognized when it is already too late, or when more power is required than usual, or when the battery is discharged slightly lower than usual. For example, in autumn, when the solar system is running low, the nights are getting longer and more electricity is needed for lighting and heating. Autumn is the time when it is usually noticed that an RV battery could not be useful anymore.

There are two possible causes of a battery failure

1. Cell closure
One or more cells in the battery have a short circuit and therefore can not be charged. It is easy to test if there is a cell leak in a lead-acid battery. The battery must be fully charged to maintain a voltage of 12.8-13V. So if the battery voltage is below 12V after 1 hour, there will likely be a cell leakage. In most cases, a cell deadlock is also recognized by the fact that the charger does not reach the end of charging voltage, the battery heats up a lot and it even smells like rotten eggs (the supply battery is boiling).

In case of a slight cell closure, however, it may happen that the cell already works but still discharges faster. A fully charged battery must always have a voltage of 12.8V after days. (Starter batteries 12.5-12.6V)

2. Age-related failure of the mobile home battery
A lead-acid battery loses a small amount of capacity with each discharge from day one. Just like a car tire with every kilometer loses a little profile. However, this wear is noticed as a regular user only when the capacity of the battery has dropped so low that it is no longer sufficient for proper operation, or just in autumn or winter when more capacity than in summer is needed.

Check the defective motorhome battery?

I am always called to campers with allegedly defective batteries and not the battery is broken. Therefore, I would like to explain to you know how you can find out for yourself whether your battery is really broken, or maybe your charger is not working correctly, or not at all. The essential requirement is a reasonable multimeter, with digital voltage display, and knowing how to operate it. 

Make sure the battery is fully charged

If the battery lasts only two hours of television in the evening, there may be two reasons. Either she was not fully charged, or she is just broken. Therefore, it is essential first to charge the battery to 100%. I know this is a bit time consuming because you have to stay with the RV, but it’s the only way.

Those with battery computers have it much more comfortable here because they can easily read all values ​​on the monitor. Motorhomes that have a current indicator (ammeter) built into the control panel are also beneficial. Without this current display, the result will be a bit more inaccurate. You can have a look at our Best AGM Battery Reviews

  1. Battery voltage measurement before you turn on the charger in the camper makes it easier for you to see if the charger is working.
  2. Charge the battery: Plug in the camper at the 230V shore power. Now the voltage on the battery has to increase. If she does not do that, you have a problem with the charger.
  3. After the first big jump of a few tens of volts, after the charger has been switched on, the voltage will slowly increase. Depending on the state of charge of the battery, this may take until the absorption voltage is reached.
  4. If the battery was already charged before, the voltage is very fast to z. For example, 14.3 volts (the actual value can be found in the user manual of the charger).
    The weaker the battery was before, and the worse your condition is, the longer it takes for your charger to reach that voltage. Therefore, you may need some patience. It is essential that you observe how the tension increases. Because when the absorption charge is complete, the charger lowers the voltage to 13.6-13.8V and you will never know if the charger is working correctly. If you look for your battery the next day, you’ll see that voltage there, but you do not know if the charger has reached the critical absorption voltage of over 14V or not. Therefore stick to it, or check the values ​​such as voltage and current (if possible) at least every 15 minutes. The best way to measure with the multimeter directly on the battery, or
  5. When the absorption voltage has been reached and has also taken some time, the array should be full. Or at least pretty full. The body battery must not be warm or even hot!

A full lead acid battery can be recognized as follows:

The battery voltage is above 14V (see the characteristic of the charger), and the charging current is lower than 2% of the capacity of the battery. Example of a 100Ah GEL battery: Voltage at the battery 14.3V Charging current has dropped to 2A. You can assume that the battery is full now.

Now we have a more definite starting point to test the battery reliably. The charger works correctly; the camper battery is fully charged. She usually has to be able to supply a few hours of electricity now.

Battery test

Discharge test with battery computer

For example, an 80Ah gel battery must be able to deliver a current of 4A for 20 hours. After that, she is unloaded. After 10 hours, it is logically 50% discharged, and you can test this value yourself. With a battery computer, which can also show the consumed amp hours (Ah), such an unloading test is quite simple. Switch on as many consumers as light and TV in the motorhome until about 1/20 of the battery capacity is applied as a discharge current and run. Now please check the battery voltage every 15 minutes. When reaching 11.8V, then turn off everything and let the batter rest for 30 minutes.

EXAMPLE: 80Ah battery: 20 = 4 amps >> run a 4 amp device (48 watts: 12V = 4 amps), for example a fan, lights, TV etc.

After that, the battery voltage should be about 12V. Now you can see on the battery computer, how much ampere hours were consumed from the battery. This value times two equals your remaining capacity.

Discharge test without battery computer

It works without a battery computer, just not beautiful.

Please remove the fully charged battery for testing. It is essential that you have a defined load. For example, a light bulb with 55 watts from the Schweinwerfer. ATTENTION that gets very hot and must not touch anything! Risk of fire! Therefore, remove the battery and place it on a non-combustible surface. For an 80Ah battery, as mentioned above, the discharge current should be about 4A. A 55Watt H4 halogen bulb needs about 4.4A at 12.5V.

You now connect the bulb directly to the battery and record the start time. Now you should check the battery voltage every 15 minutes. When reaching 11.8V, the lamp is disconnected. The number of hours x 4,4A will now give you the remaining capacity of the battery. A defective battery will usually collapse after only a few hours. A clear indication that you can buy a new battery.

If your mobile home battery is defective, the discharge attempt will probably be made quite quickly, because the voltage will collapse after a short time! That the energy after the breakdown rises again to over 12V is quite reasonable. Our Best Trolling Motor Battery will help you to choose the best one.

Revive Defective Supply Battery?

Battery pulse is the keyword to which I am repeatedly addressed. It is like this: Batteries that can not be fully charged often and for a long time and therefore are subject to certain sulfation can be revived with a battery pulse. A battered battery will not be able to restore a battery pack, nor batteries with a cell dead end.

Battery test in the workshop – quick check

Very important: Battery Quick Test Devices can only test a battery for stability (high impedance or not). Worn out batteries with only a small capacity are not detected. The devices only check the balance of a cell and not the size. I’ve had customers who have ATU certified a 100% good battery, and still sat 2 hours after sunset with an empty array in the dark camper. The battery bank with 400Ah had only 15Ah remaining capacity. With this capacity, you could quickly start a car, but not very long maintain the power supply for a motorhome.

Consultation with battery suppliers showed that factory similarly tested batteries as I have described here. Of course, there are measuring devices in the five-digit price range that can still record and check a few more values. But for a simple test, my discharge attempt described above is quite enough. You can keep your RV and RV battery good by using the Best RV Cover for The Money

I could help you with this article. Help others by sharing this article or passing on the link. I do not mind and would even be happy about it, which is not allowed to copy this text!

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