Battery Charge and Battery Discharge Indicator

Eye on the battery

Some car batteries are equipped with a charge indicator, often called an eye. It is usually green to indicate that the battery is fine, red to indicate the need for charging, and white or black to indicate the need for a water refill. Many drivers make the decision to service the battery based on the built-in indicator. However, its readings do not always correspond to the actual condition of the battery. You can learn about what is inside the battery gauge, how it works and why it cannot be trusted unconditionally in this article.

Where is the battery peephole located and how does it work?

The battery indicator peephole from the outside looks like a transparent round window that is located on the top cover of the battery, most often near the center cans. The battery gauge itself is a float-type liquid areometer. The operation and use of this device is described in detail here.

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The principle of operation of the battery charge indicator is based on measuring the density of the electrolyte. Under the peephole on the lid there is a light guide tube, the tip of which is immersed in acid. In the tip there are colored balls of different materials, which float up at a certain density of the acid that fills the battery. Thanks to the light guide, the color of the ball is clearly visible through a window. If the eye remains black or white, it indicates a lack of electrolyte and the need to refill with distilled water or a faulty battery or indicator.

What Battery Charge Indicator Color Means

The color of the battery charge indicator varies with the battery manufacturer. Although there is no single standard, the following colors are most commonly seen in the gauge:

Battery charge indicator colors

  • Green – battery is 80-100% charged, electrolyte level is normal, density of electrolyte is above 1,25 g/cm3 (∓0,01 g/cm3).
  • Red – charge level is below 60-80%, the electrolyte density is below 1.23 g/cm3 (∓0.01 g/cm3), but its level is normal.
  • White or black – the electrolyte level has dropped, it is necessary to add water and charge the battery. This color may also indicate a low charge level.
A step on the wheel or how to reach the trunk.

Precise information about the color of the indicator and its meaning is contained in the battery passport or on the top of the battery label.

What does the black battery indicator light mean?

Black battery indicator black peephole

The black peephole on the battery can appear for two reasons:

  1. Battery capacity has dropped. This option is suitable for batteries with no red bead in the indicator. Because of the low density of the electrolyte, the green ball does not pop up, so you see black on the bottom of the light guide tube.
  2. The electrolyte level has dropped – because of the low acid level none of the beads can float to the surface. If according to the instructions in such situation the indicator should be white, it means that it is contaminated by the products of battery plate decay.

Why does the battery gauge show incorrectly?

Even among conventional areometers, float-type instruments are considered to be the least accurate. This also applies to the built-in battery gauges. Listed below are the options and reasons why the color of the battery gauge does not reflect the actual condition of the battery.

How the battery indicators work

  1. A discharged battery may still show green in cold weather. The density of the battery increases as the temperature decreases. At +25°C and a density of 1.21 g/cm3, corresponding to a charge of 60%, the eye of the indicator would be red. But at -20°C the density of electrolyte increases by 0,04 g/cm3, so the indicator remains green even if the battery is half discharged.
  2. The indicator reflects the condition of the electrolyte only in the can in which it is installed. The level and density of the fluid in the others may be different.
  3. After topping up the electrolyte to the correct level, the indicator may not show the correct readings. The water will naturally mix with the acid after 6-8 hours.
  4. The indicator may become cloudy and the beads in the indicator may become deformed or stuck in one position.
  5. The eye will not let you know the condition of the plates. Even if they are crumbled, shorted or covered with sulfate, the density will be normal, but the battery will not actually hold a charge.
The charger attachment or how to recover the battery

For the reasons described above, you should not rely solely on the built-in indication. In order to reliably assess the condition of a serviced battery, the electrolyte level and density in all banks must be measured. Charge and wear of a maintenance-free battery can be checked with a multimeter, a load fork or a diagnostic tool.

Why does the gauge on the battery not show green after charging?

Battery Charge Indicator Design

Often there is a situation when the peephole does not show green after charging the battery. This occurs for the following reasons:

  1. The beads are stuck. To release, you need to tap on the window or if possible unscrew the areometer and shake it.
  2. Destruction of the plates has contaminated the indicator and electrolyte, so the bead is not visible.
  3. When charging, the electrolyte has boiled out and the electrolyte level has dropped below normal.

Frequent Questions

What does the eye on the battery indicate?

The color of the gauge on a battery indicates the current condition of the battery, depending on the electrolyte level and density.

What color should the color of the gauge on a battery?

When the electrolyte level and density of the battery is normal, the battery indicator should illuminate green. Keep in mind that sometimes, for example in freezing temperatures, this may not reflect the actual condition of the battery.

How does the battery charge indicator work?

The charging indicator works on the principle of a float areometer. Depending on the density of the electrolyte, colored balls float to the surface, the color of which is visible through a window thanks to the light-guide tube.

How do you know if the battery is fully charged?

This can be done with a voltmeter or a load fork. The built-in battery indicator determines the density of the electrolyte with a low accuracy, depending on external conditions, and only in the bank where it is installed.

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Vehicle Battery Charge Indicator

Battery indicator is an indispensable device for car owners. Its relevance increases many times, when the car suddenly refuses to start on a cold winter morning. Some start calling friends, others ask to “light” the battery, others doubt the condition of the battery.

Vehicle Battery Charge Indicator

Why do you need a battery charge indicator?

The car battery is designed with six batteries. They are connected in series and deliver 13-13.5 V. The longer the battery is used, the less time it can hold a charge.

Why do I need a battery charge indicator

The situation is aggravated during the cold season, when the “heater” is actively used. Even leaving the parking lights on for the night can completely “kill” the battery.

Modern batteries are equipped with a device that determines and shows the level of charge. The built-in discharge indicator of the car battery is located on the top side of the battery.

Seeing the red peephole, the car owner immediately understands that the battery needs charging. If the peephole is green, then there is nothing wrong with the battery and there is no need to worry.

How it works

Under the eye of the indicator there is a built-in aerometer – a device that determines the density of the filled electrolyte. Depending on the measured parameters, the device informs the owner of the car that it needs urgent recharging.

Working Principle

The aerometer is a tube with a colored spherical float at the end. When the charge is good, the density of the electrolyte is high and the ball pushes upwards. It is observed by the owner of the car through a peephole.

When the battery charge is low, the density of the liquid decreases, the green ball sinks and only the black tube is visible in the peephole.

In some batteries an additional red balloon serves as an indicator. As the density decreases, it goes up when the green ball sinks.

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In addition to a low charge in the battery, the electrolyte level may be too low. In this case, the surface of the liquid is observed in the eye and the car battery charge indicator shows a white color.

Indicator Diagram

The electrical circuit of the 12-volt battery charge level indicator contains no stabilitrons, no complex microcircuits or transistors. It consists of series connected resistors and LEDs.

Indicator diagram

The operation of the device is based on the initial lighting voltage of the LED, which is a semiconductor.

When switched with resistors in series, each LED lights up after the voltage exceeds the sum of the LEDs on the corresponding circuit segment.

The opening or lighting voltage limit of the LED is in the range of 1.8-2.6 V, depending on its model. Each successive element starts to light up after the previous one has been turned on.

What are the Indicators

What kind of indicators are

Most batteries are equipped with a built-in sensor, the operation of which is based on determining the density of the filled electrolyte. It has a high accuracy and is inconvenient to use.

To see if the indicator is lit in different operating modes, you have to lift the hood of the car every time.

There is a huge choice of devices in stores, which differ in functionality, design, use of float or LED. Factory-made indicators are divided according to several criteria.

According to the way the device is connected:

  • to the onboard network;
  • to the cigarette lighterighter.

According to the method of signal output:

  • analog;
  • with digital indication of battery charge.

All types of devices have a simple principle of operation – battery charge measurement and information output in an understandable form for the user.

Color designations

Color designations

The battery gauge assumes four color indication options. Each of them corresponds to a certain level of charging:

  1. Green. This color indicates that the battery is fully charged, recharging is not needed in the near future. The car can be used as usual.
  2. A red light on the car battery is an alarm indicating that an urgent recharge is required.
  3. Black signals the same problem as red. It means that the density of the electrolyte is low, the green ball has sunk to the bottom and only the blackness of the tube is visible in the peephole. Urgent recharging is required.
  4. White peephole indicates low electrolyte level. The problem can be solved by yourself – the battery is disassembled and distilled water is added to the battery.
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Battery charge indicator with your own hands

If you have free time, the charge indicator can be made at home. The device will monitor the work of the battery at volt characteristics of the network from 6 to 14 V.

Battery charge indicator with your own hands

The principle of operation of the device is the same as that of models made at the factory and sold in auto stores.

To make the device you will need:

  • printed circuit board;
  • DC 557 and BC 547 transistors;
  • Two regulators for 9.1 and 10 V;
  • resistors – 2×1000 Ohm, 3×220 Ohm and one 2200 Ohm;
  • LEDs of different colors – blue, red and green.

Prepared in advance elements are assembled according to any of the schemes, which can be easily found in reference books or on the web.

All parts should be placed on a printed circuit board so that they occupy as little space and volume as possible. Before soldering, the LED elements should be checked for color and contact matching with a tester.

Adjustment of the circuit is done by connecting it to an adjustable power supply and checking that the colors of the elements are displayed correctly in the desired mode.

The LEDs should be soldered to special wires and not directly to the board. This will allow you to compactly and conveniently place the indicator device inside the car dashboard.

Independently assembled board should be attached to the inner surface of the dashboard, connect to the cigarette lighter or on-board network. LEDs soldered to the wires are led to the outside of the panel.

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