My Battery Tender Flashes Red To Green - What Does That Mean? - The Gadget Buyer | Tech Advice (2023)

Battery Tenders are a great resource to have equipped in any vehicle, but what does it mean when the lights start flashing red and green? There is nothing worse than trying to start your car engine only to find that the battery is drained, which is why so many drivers rely on Battery Tenders for support. However, some people have been reporting that their Battery Tender starts flashing red to green, which could imply that there is an issue with your battery.

My Battery Tender Flashes Red To Green - What Does That Mean? - The Gadget Buyer | Tech Advice (1)

Table of Contents

  • What does it mean when a battery tender flashes from red to green?
  • Why Does My Battery Tender Flash Red to Green?
    • 72-Hour Safety Timer
      • Large Battery
      • Standard Battery
    • Defective Battery
  • What do the Other Lights on My Battery Tender Mean?
    • Red Light
    • Amber Light
    • Green Light

What does it mean when a battery tender flashes from red to green?

If a Battery Tender is flashing red to green, it means that your battery has either reached its 72-Hour Safety Timer and is in maintenance mode – or that the battery is defective. The 72-Hour Safety Timer implies that you are charging a large battery or that there is a connection resistance.

Car batteries generally last at least 3 to 4 years, but even during their prime, they can often cause trouble for you when you need to drive your vehicle. Whether you are rushing out the door to head to work or driving out in the countryside, a car battery that dies on you when you need it the most is frustrating to deal with.

This can particularly be the case if you live in a region that gets colder weather where temperatures drop below freezing, as this can make drained batteries a constant theme in your life. Luckily, you can avoid the headaches that come with a drained battery by using a Battery Tender. This is essentially a support system that prevents the likelihood of your battery draining on you.

However, your Battery Tender is also equipped with a color-coded light system to indicate the condition of your battery – with a red and green flashing light potentially implying that something is wrong.

To help you understand this further, we are going to take a closer look at what the flashing red and green light on a Battery Tender means.

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After extensively researching Battery Tender maintenance issues and protocols, I have been able to gather enough information to determine what a red and green flashing light indicates. My research has shown me that you should always confirm the color-coded system of your Battery Tender, as this can often vary depending on the model that you are using.

Why Does My Battery Tender Flash Red to Green?

Battery Tenders are designed to be there for you when you need them the most. This battery-supporting device ensures that you never have to deal with a dead battery when starting your vehicle.

With that being said, if you want to count on your Battery Tender through thick and think, then you need to be aware of what the color-coded lights on the device indicate.

A lot of people have reported that their Battery Tender starts to flash from red to green.

There are multiple different reasons behind a red and green flashing light on a Battery Tender – with one implying that there is nothing to worry about and the other indicating a bad battery. However, you should also keep in mind that Battery Tenders are made by more than one manufacturer and that each brand could have potentially designed its own color-coded system.

Although the colored lights on most Battery Tenders may mean the same thing, you should still have the manual for your specific model handy when assessing the condition of your vehicle’s battery.

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Let’s dive into why your Battery Tender flashes from red to green.

My Battery Tender Flashes Red To Green - What Does That Mean? - The Gadget Buyer | Tech Advice (2)

72-Hour Safety Timer

One reason behind the red and green flashing lights on your Battery Tender is that the 72-Hour Safety Timer has been activated. Most Battery Tenders are only designed to support a certain amount of voltage.

Generally speaking, a Battery Tender will try to reach a charge level of 14.75 volts as its target. If the Battery Tender detects that the voltage has not reached 14.75 volts within 72 hours from when the charging process began, it will switch into maintenance mode.

This is a safety feature installed in most Battery Tenders and it does not necessarily imply that there is anything wrong with your battery.

When maintenance mode is activated, the battery will stay at 13.2 volts. Once this happens, the Battery Tender’s light will start flashing from red to green.

Large Battery

If the 72-Hour Safety Timer was initiated on a large car battery, then you probably do not have anything to worry about. A large car battery will take longer to charge and the red and green flashing lights could simply imply that the battery has not reached its maximum charge capacity yet.

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Regardless, given the obscurity of what a red to green flashing light could imply, it would still be wise to test your large battery to ensure that it is in good working condition.

Standard Battery

A 72-Hour Safety Timer on a standard car battery could mean that there is an issue with either the connection or the battery itself. A connection issue could be due to faulty wiring or if there is resistance to the connection in your battery.

Defective Battery

Although dealing with a defective battery is never a fun experience, it is better that you find out about it from your Battery Tender before you hit the road, rather than when you are stranded out in the middle of nowhere.

The red and green flashing lights on your Battery Tender often indicate that your battery is defective. You may still be able to get away with using your battery for the short term, but you should ultimately start coming to terms with the fact that it will need to be replaced soon. More often than not a defective battery is related to the following issues:

  • Corroded battery terminal
  • Sulfated battery

Sulfated batteries can potentially be reversed with a slow charge – whereas corroded batteries may be fixed with a vinegar solution. With that being said, the best way to avoid a defective battery is to prevent it from happening in the first place by taking care of it.

What do the Other Lights on My Battery Tender Mean?

You Battery Tender is designed to have a variety of different colored lights to tell you what condition your battery is in. This makes observing your battery health incredibly easy so that you always know how to maintain it.

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If you have noticed that your Battery Tender is flashing from red to green, you will most likely be curious about what the rest of the lights on the device indicate.

Red Light

When your battery is plugged in, connected, and charging, you will see a red light on your Battery Tender. This will let you know that everything is connected properly and that your battery is receiving a stable charge.

Amber Light

You will see an amber light on your Battery Tender when the device is powered on and plugged in. The Battery Tender will have to be plugged into a wall outlet that is delivering AC power to the device.

Green Light

A green light will start to flash when your battery is almost fully charged – with most Battery Tenders this is at 80%. Once the battery reaches this stage, it will start to receive a smaller charge until it gets to 100%.

The red light will continue to flash while the green light is on and it will turn off once the battery is fully charged – with only the green light staying on.


What does it mean when battery tender is flashing? ›

flashing indicates that the battery charger has AC power available and that the microprocessor is functioning properly. If the amber LED continues to flash, then either the battery voltage is too low (less than 3 volts) or the output alligator clips or ring terminals are not connected correctly.

Why is my battery tender junior flashing red and green? ›

RED & GREEN ALTERNATING LIGHTS: When the red and green lights alternate, then either the 72- Hour Safety Timer has been activated or the battery is defective.

What does it mean when a battery flashes green? ›

Short green flash = less than 80% charged. Long green flash = more than 80% charged. Solid green light = 100% charged.

Why is my trickle charger blinking red and green? ›

The LED on the battery charger will flash between red and green after it has completed its charging cycle. This can occur with Nickel Metal Hydride batteries (PTS360) that are still within their warranty period (1 year). This condition does not indicate an equipment failure.

What does it mean when a trickle charger is blinking? ›

The CHARGE light may flash for the following reasons: The environmental temperature is too cold to charge the battery pack. The battery pack has not been used for a long time. There is a poor connection between the battery and charger.

How do you tell if your battery tender is working? ›

If the battery is fully charged, then the Battery Tender Plus battery charger's green light will be on. Once the AC power is removed from the Battery Tender Plus battery charger, the green light will go out and the charger not have any effect on the battery.

Can you tell if a battery is dying? ›

Slow engine crank.

This is probably one of the most common symptoms of a dying battery. The engine pulls amperage from the battery each time it starts. If your battery is close to dying, you will likely find your engine slow to crank. If you hear your engine cranking slowly, bring the vehicle in as soon as possible.

How can you tell if battery is bad? ›

Signs you have a bad battery
  1. The car is difficult to start.
  2. Once started, the car doesn't hold a charge for very long.
  3. Dim or flickering taillights and headlights.
  4. Dim interior and dashboard lights.

How do you tell if a battery is bad with a battery charger? ›

If your battery is: Reading 0 volts, chances are the battery experienced a short circuit. Cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell. Fully charged (according to the battery charger) but the voltage is 12.4 or less, the battery is sulfated.

Does a battery tender charge a dead battery? ›

If you try to charge a dead battery having a voltage below 3 Volts, the Battery Tender® Junior charger will not start. An internal safety circuit prevents the charger from generating any output voltage unless it senses at least 3 Volts at the charger output.

What happens if you leave a trickle charger on too long? ›

A: If you leave the charger connected continuously, even at a mere 2 amps, the battery eventually will die. Overcharging a battery causes excessive gassing — the electrolyte gets hot and both hydrogen and oxygen gas are generated.

Why is my battery blinking red and not charging? ›

Generally, this occurs when the charger does not receive a signal from the batteries, in other words there is a break in the connection between the charger and batteries.

Can you overcharge a battery on a trickle charge? ›

Trickle charges employ the use of a battery regulator to regulate charging rate and prevent overcharging, charging your vehicle's battery at a rate similar to the rate at which it self-discharges so as to maintain full battery capacity. Charging at too fast of a rate or overcharging can cause damage to the battery.

Can you leave a trickle charger on a battery all the time? ›

Some trickle chargers will allow you to leave them overnight, while some up to 48 hours. Leaving electrical units like this unattended could also pose a potential fire hazard if they short circuit.

What should a battery tender read? ›

In most cases, a 12 volt lead-acid battery, at 100% SOC, will have a rest voltage between 12.8 and 13.1 volts. That means an effective float voltage need only be as high as 12.9 to 13.2 volts. However, most Battery Tender® battery chargers have float voltages between 13.3 and 13.5 volts.

How long can you leave a battery tender on a battery? ›

It will keep the battery charged at 100% even if you don't use your bike for weeks or months. It is recommended that you can leave the battery maintainer connected for months and get a 100% charge when you have to use your bike.

How do you reset a battery tender lithium ion battery? ›

To activate the battery simply press the BATTERY RESET BUTTON located at the end of the Quick Disconnect (QDC) charging harness for ONE second.

Can you leave a battery tender connected all the time? ›

So, can you really leave your battery maintainer on all the time? Fortunately, the answer is yes! Battery maintainers are designed for constant and long-term use. When used correctly, they should be perfectly safe to use as long as you need.

How do you tell if its your alternator or your battery? ›

Jumpstart your car. If you can turn the engine on, but it dies shortly thereafter, your car alternator likely isn't able to charge the battery. On the other hand, if you jumpstart the car and later on it fails to start on its own, it's likely a dead battery.

How do I know if my car battery needs replacing? ›

How to Know When it is Time to Replace Your Car Battery
  1. 4 Signs It Is Almost Time For a New Battery.
  2. 1) Your Battery Struggles to Combat Seasonal Challenges.
  3. 2) Your Car Has Been Sitting For Too Long.
  4. 3) Your Vehicle Struggles When Starting.
  5. 4) Your Battery Is Older and Triggers a Dashboard Light.

What does a weak battery sound like? ›

> Clicking sounds - If you hear a clicking sound when you attempt to start your vehicle, then it is possible that your vehicle has a flat or weak battery. The clicking sound could be the starter motor, and it means that there is not enough power getting to it.

What are the symptoms of an alternator going bad? ›

7 Signs of a Failing Alternator
  • Dim or Overly Bright Lights. ...
  • Dead Battery. ...
  • Slow or Malfunctioning Accessories. ...
  • Trouble Starting or Frequent Stalling. ...
  • Growling or Whining Noises. ...
  • Smell of Burning Rubber or Wires. ...
  • Battery Warning Light on Dash.
24 Aug 2020

What can drain a car battery when the car is off? ›

What may drain a car battery when it's off are things such as interior lights, door lights, or even bad relays. While your engine runs, the alternator recharges the battery — which is why you typically don't have to worry about the battery dying while you're blasting the radio on your drive to work!

How do you know if battery tender is charging? ›

RED LIGHT ON STEADY – When the red light is steady, a battery is connected properly and the charger is charging the battery. The red light will remain on until the battery is completely charged.

How can I tell if my battery tender is working? ›

If the battery is fully charged, then the Battery Tender Plus battery charger's green light will be on. Once the AC power is removed from the Battery Tender Plus battery charger, the green light will go out and the charger not have any effect on the battery.

Will Battery Tender start dead battery? ›

If you try to charge a dead battery having a voltage below 3 Volts, the Battery Tender® Junior charger will not start. An internal safety circuit prevents the charger from generating any output voltage unless it senses at least 3 Volts at the charger output.

Can you overcharge with a battery tender? ›

Yes, while the current they supply is much smaller than a standard charger, a trickle charger can still overcharge your battery if kept on for too long. A battery maintainer is a kind of "smart" charger that will only supply current when your battery's voltage drops below its ideal level.

How long does it take for a battery tender to charge a car battery? ›

Car batteries usually hold 48 amps, so it will take about 12 hours to reach a full charge using a 12 volt charger. It takes around 30 minutes for an electric vehicle to charge to 80%.

How long can a car sit on a battery tender? ›

Typically, your car can sit about four weeks to two months without driving before the battery dies.

How long does it take a battery tender to charge a dead battery? ›

So it will take 6 to 8 hours for the green light to come on. Fortunately, the Battery Tender Plus has the ability to continue to supply its full current even after it has switched over to the lower, float, maintenance charge voltage of 13.2 volts.

How do I reset my battery not charging? ›

Try booting without the battery

Unplug the power adapter and then press and hold the laptop's power button for at least 15 seconds. This should reset the laptop and drain any residual charge in the power supply. Now, with the battery still removed, plug the power adapter in and see if you can start the laptop.

How can you tell if your battery is getting weak? ›

If the cranking of the engine is sluggish, like your vehicle is harder to start on cold mornings, it starts inconsistently, or there's no sound and interior lights when you try to start, suspect a failing battery, a loose or corroded connection or electrical draw.

Is it OK to start a car with a battery tender connected? ›

A: Yes you can start your car when hooked to Tender. Care must be taken to make sure that the cable are clear of all moving parts under the cars hood. Keep in mind that the tender will not jump start a car and if the battery is too drained it will not charge it.

Can I leave battery tender on all winter? ›

Make sure you don't leave them hooked up to a charger all winter! This can be dangerous, and will damage your batteries. Once charged, the self discharge rate of the batteries will keep them up to snuff until June for sure. With such controversy over the subject, we are listing towards Ed's educated advice.


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