Bullseye indicator on Mercedes battery
 

My friend was over working on his 1999 C230. He has a Mercedes battery he got from the dealer about 5 years ago and it is working fine. I suggested he check the water. But it looked like this (picture attached). We contacted the dealer and after much research they stated it is a non serviceable battery. Then I asked about the bullseye indicator (next to the "made in Germany" sticker). I was concerned because it is dark which on some other batteries would indicate low water:

For example this is what Motorcraft says about theirs:

1. Green: battery is charged and the acid level is good.
2. Yellow: Battery is partially dis-charged and the acid level is good. Re-charge the battery or drive the vehicle.
3. Red: Battery is dis-charged and the acid level is good. Charge the battery.
4. Clear and bright: Acid level is low!!! Add distilled water if possible. If not, change out the battery. Do not charge or jump start the battery!!!

However, the dealer stated that dark is OK, and white means it is bad.

The battery PN is A9069820008

Does anyone have experience with these? I am thinking it needs some water.

Thanks

The battery on my Honda was green/black/red depending on the state. When healthy or fully charged, it was green. When partially discharged, black. When discharged, red. Not sure about the Mercedes battery, but they're usually a function of the specific gravity of the acid in the cells and the balls "float" at different gravities based on charge state. If your battery is similar to the type stated above, it maybe getting towards the end of its life. A black window in a battery of that variety can still give good service for a period of time, but it's capacity will be reduced.

The battery shown in the picture appears to have caps, but whether or not they come off is unknown. Serviceable type batteries tend to have a cap for each cell (6) or a cap for each group of 3 cells that is raised with a pry slot for a screwdriver.

It's worth noting that when a battery is low on water it's on borrowed time. The most common cause being overcharging.

5 years on a battery is about the expected life.

Keep it charged and replace it when symptoms of a weak battery (low voltage, slow cranking) occur.

Forget the indicator. I've had batteries go 4 or 5 years after the indicator shows "bad" and I've had bad batteries with a "good" indicator.

Most indicators merely reflect cell fluid level or acidity not whether there is adequate voltage or continuity between the cells.

The information that the dealer gave is correct. Unlike other manufacturers, the indicator does not show state of charge but fluid level.

It would be nice if Mercedes provided this information IN WRITING.

The dealer said this was a Sprinter battery (?) so I looked at the Sprinter owners manual. Nope, that shows the 6 individual caps (and also says nothing about checking the water or anything else.)

It is a bit shocking that the battery says nothing about the window status on the label. Generally a window-style battery will have some sort of legend to tell you what it is you're looking at!

There is usually a label but it looks like it could easily come off.