Why UPS Battery Not Charging

Why UPS Battery Not Charging [Reasons & Fix]

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Inside a UPS, there are lots of things going on. For example, there are cooling systems, circuits, power supply, or wiring. If I make it simple, there are only three primary units. One is charging that processes AC and provides DC as output. Another is the battery where DC is stored.

Lastly, the inverter system converts DC to AC and supplies it to your devices. However, are other systems like the cooling system and safety system enhance the overall performance of the UPS.

However, these systems are dependent on each other. So, when a system gets corrupted, another system can’t work well. Same for the charging system. It fails mostly when the other system gets corrupted. How?

You will learn after finishing the post.

Why UPS Battery Not Charging

A UPS battery not charging primarily because of a dead battery. Besides, electrical faults like loose connections, disconnections, burning, or melting can also cause charging errors.

However, let’s elaborate on these reasons.

  1. Exhausted battery: It’s a common problem that every user face while using a UPS. Most of the time, UPS errors occur due to a dead battery. Same for the charging system. The UPS won’t charge at all when the battery is exhausted.
  1. Loose connections: Sometimes, everything is okay, but the UPS still doesn’t charge. In this case, the wiring can be the culprit. If there are loose connections or disconnection, the UPS battery won’t charge. Here, the wiring can get damaged inside and outside the UPS.
  1. Burnt rectifier: A rectifier does the job of converting AC to DC. DC is what is stored on the battery. So, when the rectifier is burnt, the current won’t convert and won’t be stored in the battery. Thus, the UPS battery can’t charge.
  1. Melt fuses: There are a few fuses inside the UPS. They are used to save the appliances from short circuits. While doing so, they get melted. Thus, the circuit becomes incomplete, and the charge can’t reach the battery. As a result, the UPS battery stops charging.

Preventive Care For UPS Charging System

How to fix UPS charging system

Taking preventive measures is more important than a fix here. Not only for UPS, but any kind of electronics also needs some basic maintenance. It’s a must if you expect excellent performance and the long life of an appliance. So, here I have come up with some maintenance tips for UPS to keep the charging system fit.

  1. Cooling system: You can see rectifiers are getting damaged due to overheating. So, you must cool it down to save the components. For that, you have to keep the cooling system fit. Regularly check if the cooling fan is functioning well or not. Fix it if there are any problems. Besides, you can use Thermal Paste in certain places to reduce heating.
  1. Battery maintenance: As the battery itself can be a reason for charging, you must keep it healthy. For that, avoid overload and replace the water. It’s good to change the water every 2 months. Thus, the battery performance gets enhanced, and it charges and discharges well.

How to Fix UPS Charging System

Why Cyberpower UPS won't turn on after power cut

As there are many reasons for charging failure, one solution is not enough. Here are 4 different tips to solve 4 different problems. Follow the tips which are relevant to your UPS problem. Here you go.

Tip-1: Swap the rectifier

The rectifier is one of the most essential parts of a charging system. It works as the current conversion unit of the charger. So, the charging system when it is burnt out. However, let’s know how to swap the rectifier in UPS.

  1. Firstly, remove the old rectifier. For that, open the UPS casing and bring out the motherboard. Now, melt the downside prongs of the rectifier by soldering. Then pull the rectifier diode. You can do it with a small Needle Nose Plier. While removing the rectifier, make sure you don’t damage the motherboard,
  1. Secondly, get a Spare Rectifier and replace the old one. However, make sure the rectifier is compatible with the UPS. You don’t need to understand technical information. Just ensure the new one’s specifications match the old one. Anyway, join the rectifier with soldering now.
Caution: Be careful while swapping the rectifier. If you join it incorrectly, the UPS won’t work. You can follow the previous setting to avoid misplacement. Take help from a professional if it seems complicated to you.

Tip-2: Change blown fuses

An electrical circuit becomes incomplete when the fuses get blown. So, you must change the fuses immediately after they melt to keep the circuit complete. So, get some Spare Fuses and replace the old ones.

However, you should identify the fuse compartment before doing it. Generally, it is situated on the backside of the UPS. If I say precisely, it is placed under the sockets. Anyway, rotate and pull the fuses to bring them out of the UPS. Now check if they are okay or melted.

Replace them if they are blown. For that, insert the new fuses inside the compartment. Then push and rotate, and it will be all set. Lastly, check if the UPS battery is charging or not. If it is not charging, there may have other problems.

Tip-3: Fix the wiring

If the UPS doesn’t get fixed after swapping the rectifier or changing blown fuses, there may have wiring problems. When I talk about wiring problems, it includes loose connection, disconnection, or damaged cable. So, you will need some spare wires and a Soldering Iron to fix these problems. However, let’s go step by to fix wiring problems.

  1. Firstly, keep the UPS on AC mode. Then identify the connection points and do the voltage test. For that, take a Multimeter and check if the current is passing through the wiring or not.
  1. Secondly, if the current is not passing, you must rectify the electrical error. For that, you have to look for disconnection or loose connection and fix it with soldering. If the wiring is damaged from inside, you should replace the cable. Otherwise, a short circuit or bypass can occur there.
  1. Lastly, test the UPS. Check if the battery is charging or not. If it is still not charging, repeat the above steps or replace the battery.

Tip-4: Replace the battery

Tips for taking care of UPS battery

When the battery gets exhausted, there is no other way than replace it. It will require a simple process to replace a battery. I have discussed it earlier on my UPS replacement guide, so not gonna repeat it.

Frequently asked question

How do I know if UPS is charging?

Most of the UPS comes with a display or charging indicator. Thus, you can know whether the charging or not. But, for confirmation, you need to do a voltage test. You will need a Multimeter for this job. Now, remove the battery and set the voltmeter with prongs. Then, measure the output voltage produced by the charging system.

Should the UPS be on while charging?

It doesn’t matter whether the UPS is on or off while charging. For other appliances, charging is discouraged while discharging. But it does not apply to UPS. There is no such case where UPS gets damaged due to simultaneous charging-discharging. So, you can keep the UPS on or off while charging.

Can UPS charge itself?

A UPS converts AC to DC and store it in a battery. Then DC is once again inverted to AC and supplied to the appliances. There are no chances of reversing or manipulating this process. It’s as simple as that. So, the UPS can’t charge itself. It is just charged by AC, and DC can’t charge it.


Charging a UPS is a must to keep it powered up. Otherwise, it has no use. So, trouble arises when the UPS is not charging. Now, you can bring it to a mechanic for repair. But, DIY is fun, easy, and money saver here. So, you must try the quick fix first. If the UPS doesn’t fix after it, try advanced troubleshooting. Besides, you can take help from professionals.

However, I have described the quick fix and the advanced troubleshooting. Also, the reason for charging failure is explained earlier.

Anyways, the repair works may require some components. My suggestion is to get high-quality parts and avoid cheap ones. Otherwise, the UPS can get corrupted again. I hope it won’t happen again.

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