[fsd350]

Just installed an Atlas 49 AGM battery in my e90 335d. The car had the original 90AH flooded cell battery. The spec on the new battery is 180RC with 850CCA. Like most aftermarket batteries, it does not show an AH spec. I coded the car for AGM 105AH. There are a few different formulas or speculations concerning the RC to AH conversion. The RC/2 +16A is one of them.

Here are my questions/concerns:

1. Is it better/safer for the battery to code the vehicle at a little higher OR lower AH than the actual battery spec? (true AH spec is unknown)

2. Would coding the vehicle at a little higher setting than the battery spec cause the charging system to overcharge the battery OR allow for a higher discharge before increasing the charge rate?

I may be overthinking this as it is only a 15 AH difference. I am thinking that setting the battery spec to 105ah would allow me to take better advantage of the new batteries' capacity rather than coding to 90 AH. Most aftermarket batteries in this group size fall between the 2 settings (90 AH or 105AH), if they show the true AH spec at all.

I spent some time searching the forum and could not seem to find the answer to my particular questions. Thanks guys

[histandards]

i also have this question.

My new Autocraft AGM Battery is 900CCA 160RC and doesn't list an AH. I chose 90AH when I registered it with BMWHAT. using RC/2 +16 it would be 96AH. Should I have went with 100AH? (the only two options I get on the app).

[fsd350]

Originally Posted by histandards

i also have this question.

My new Autocraft AGM Battery is 900CCA 160RC and doesn't list an AH. I chose 90AH when I registered it with BMWHAT. using RC/2 +16 it would be 96AH. Should I have went with 100AH? (the only two options I get on the app).

I ended up using 90ah rather than 105ah as 90a closer to the batteries' trating. The exact ah rating can be changed with BMW standard tools, but I decided to stop overthinking this and move on.

[matteblue3er]

Originally Posted by fsd350

1. Is it better/safer for the battery to code the vehicle at a little higher OR lower AH than the actual battery spec? (true AH spec is unknown)

2. Would coding the vehicle at a little higher setting than the battery spec cause the charging system to overcharge the battery OR allow for a higher discharge before increasing the charge rate?

Code it as the next higher capacity. This chassis likes to float the battery charge around 80%. If you put a lower spec, it will keep the battery in a discharged state. A non-AGM lead acid battery will begin to sulfate and decrease battery performance.

With that being said, I had a 90Ah AGM battery in my car for 5 years coded as a 70Ah battery. It was fine. However, AGMs can recover from a discharged state more easily than a non-AGM.

I currently have a 140Ah battery coded as a 110Ah (which is the highest capacity you can code) every couple weeks I will top off my battery with a charger.

BTW, 105Ah is not an option. I have attached a photo of the options.

[fsd350]

Originally Posted by matteblue3er

Code it as the next higher capacity. This chassis likes to float the battery charge around 80%. If you put a lower spec, it will keep the battery in a discharged state. A non-AGM lead acid battery will begin to sulfate and decrease battery performance.

With that being said, I had a 90Ah AGM battery in my car for 5 years coded as a 70Ah battery. It was fine. However, AGMs can recover from a discharged state more easily than a non-AGM.

I currently have a 140Ah battery coded as a 110Ah (which is the highest capacity you can code) every couple weeks I will top off my battery with a charger.

BTW, 105Ah is not an option. I have attached a photo of the options.

Ok, thanks or the info matteblue. That is exactly the info I was looking for. After updating to the latest datens before coding however, my options do include a 105ah AGM as an option. It was originally coded as a 90ah lead acid with the original battery. I did not check out the options before updating the datens. Maybe the d has different options as well? I will recode per your suggestions. Thanks again.

[matteblue3er]

Originally Posted by fsd350

Ok, thanks or the info matteblue. That is exactly the info I was looking for. After updating to the latest datens before coding however, my options do include a 105ah AGM as an option. It was originally coded as a 90ah lead acid with the original battery. I did not check out the options before updating the datens. Maybe the d has different options as well? I will recode per your suggestions. Thanks again.

Hmm maybe they updated it in later models. My bad