Specific gravity, checking
WARNING:
- Observe Warning and safety measures for lead acid batteries. Refer to Warnings and safety measures for lead-acid batteries .
- Always wear suitable protective clothing. Refer to Warnings and safety measures for lead-acid batteries .
NOTE:
- Audi TT equipped with the 3.2L V6 engine are equipped with an Absorbed Glass Mat (AGM) battery located in the left rear luggage compartment in the spare tire/wheel well.
- Unlike conventional lead-acid batteries, AGM batteries are completely sealed and use a fiberglass mat construction which completely absorbs the electrolyte. As a result, no excess electrolyte is present, and it is not possible to check the electrolyte level or otherwise service the electrolyte.
- If it is determined that an AGM battery is malfunctioning, replacement is necessary.
- The following procedures apply only to batteries with removable cell caps.
WARNING:
DO NOT attempt to open an AGM battery!
Special tools, testers and auxiliary items needed
- Commercially available hydrometer
- Cleaning cloths
NOTE:
- In conjunction with the "voltage under load" test, the specific gravity test gives a good indication of the battery condition.
- The temperature of the electrolyte in the battery must be at least 10 ° C.
- The specific gravity can be checked immediately after charging battery.
CAUTION:
- Dispose of electrolyte (sulfuric acid/water mixture) properly! Waste electrolyte must only be disposed of in appropriate waste disposal sites. Refer to local regulations pertaining to electrolyte disposal.
- To ensure effective sealing of the various battery cover systems, it is important to use the correct type of battery cell caps. If caps are lost or damaged, always install new caps of the same type as originally installed.
- Each cell cap must be installed with an O-ring seal.
The specific gravity must be checked in all battery cells as follows:
CAUTION:
Before beginning repairs on the electrical system
- Switch off all electrical consumers.
- Switch off ignition and remove ignition key.
- Remove all battery plugs (battery cell caps).
- Immerse end of hydrometer in a cell and extract sufficient electrolyte so that float swims free in the electrolyte.
- The greater the specific density of the extracted electrolyte, the higher the float rises
- The density in kg/dm3 can be read off the scale of the hydrometer (specific density of electrolyte)
- Read off measured value on hydrometer and compare with table:
| Charge condition in normal climates | Specific gravity in kg/dm3 |
| Discharged | 1.12 |
| Half charged | 1.20 |
| Well charged | 1.28 |
| Charge condition in tropical climates | Specific gravity in kg/dm3 |
| Discharged | 1.08 |
| Half charged | 1.16 |
| Well charged | 1.23 |
In countries with normal climates the specific gravity must be at least 1.24 kg/dm3.
- If the specific gravity is too low, charge the battery.
- After charging the battery, repeat the specific gravity test.
NOTE:
The specific gravity readings for the individual battery cells must not differ by more than 0.03 kg/dm3.
Examples of non-acceptable differences between specific gravity levels
| Battery cell: | 1 | 2 | 3 | 4 | 5 | 6 |
| Specific gravity per cell in kg/dm3 | ||||||
| Example 1: | 1.24 | 1.25 | 1.25 | 1.10 | 1.24 | 1.25 |
| Example 2: | 1.26 | 1.26 | 1.25 | 1.14 | 1.18 | 1.24 |
Example 1:
- The specific gravity in cell 4 is too low.
Example 2:
- The specific gravity in cells 4 and 5 is too low. The specific gravity readings for the individual battery cells differ by more than 0.03 kg/dm3.
- If the specifications are not obtained, replace battery.
- If the specifications are obtained, screw plugs in again.
Always use the original cell caps and check they are fully screwed in to make sure that the battery is properly sealed.
Use genuine cell caps of the same type if the original plugs are lost or damaged.
Each sealing plug must be installed with an O-ring.