Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Brief description of components
An AGM battery can be recognized by its black housing and the lack of a so-called "Magic Eye".
| Key | Explanation | Key | Explanation |
|---|---|---|---|
| 1 | Positive grid with silver alloy | 2 | Positive plate |
| 3 | Negative grid | 4 | Negative plate |
| 5 | Separator made of glass fibre fleece | 6 | Positive plate pack |
| 7 | Negative plate pack | 8 | Plate block |
| 9 | Block holder with bottom rails |
Design
The AGM battery differs from the conventional lead calcium battery as follows:
- Larger plates:
Larger plates provide for a 25 % higher power density.
- Separators made of glass fibre fleece:
These provide for up to 3 times higher cycle reliability.
This in turn improves cold starting performance, current consumption and service life.
- Gas-tight housing with pressure relief valve:
The cell plugs are welded and cannot be opened.
- Acid bound up in the glass fibre fleece:
The acid is not as previously self-contained in the housing, but 100 % bound up in the glass fibre fleece. This provides increased protection against acid leakage and thus represents a reduced risk to the environment.
Mode of operation
The AGM battery differs from conventional batteries in its non-polluting and substance-retaining behavior during charging.
When vehicle batteries are charged, the two gases oxygen and hydrogen are released by electrolysis.
- In a conventional wet lead calcium battery, the two gases hydrogen and oxygen are dissipated into the atmosphere.
- In an AGM battery, the two gases are converted back into water: The oxygen which is created at the positive electrode during charging passes through the permeable glass fibre fleece to the negative electrode. At the negative electrode the oxygen reacts with the arriving hydrogen ions in the electrolyte to form water (oxygen cycle).
In this way, the gas and thus also the electrolyte are not lost.
Only in the event of an excessively heavy buildup of gas, i.e. excessively high pressure buildup (20 to 200 mbar), does the pressure relief valve discharge the gas. In this process, the pressure relief valve does not allow any oxygen in the air to enter. Because a valve regulates the pressure in the battery, the AGM battery is also known as a VRLA battery (Valve Regulated Lead Acid).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.