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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Ah Calculation for Coding New AGM Battery



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      09-16-2020, 02:35 PM   #1
PugDaddy
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Ah Calculation for Coding New AGM Battery

So, I just installed a new AGM battery in my 2010 e93. I registered it but have not coded it yet. The battery is a Champion H8-900CHAGM. It has 900 CCA and 160 reserve capacity. I've seen various formulas for calculating the required Ah value need for coding. I contacted Champion and here is their response:

"Thank you for contacting Champion Batteries. I have attached the specifications for this battery however the Ah is a calculation this is done by doing this equation Ah=900/7.25. Ah is 124.18. Let me know if this works."

I used a different formula and came up with 96. 124 seems very high. Would it be safer to use 100? I think the worst case scenario would be overcharging...am I correct?
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      09-16-2020, 04:23 PM   #2
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Calculating AH from RC is really not possible. They are measured differently, using different loads and methods.
There are generalizations, what you're finding from the "calculators" and "formulas", but those are just best guesses.
Some say divide RC by half, some say divide by half and add 16...you can see why this is a problem. It looks like your 96AH rating was concluded by dividing RC in half and adding 16?

If the battery manufacturer hasn't tested for AH and made that info available, somewhere, then the only way for you to truly know is to perform some testing on your own.
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      09-16-2020, 05:10 PM   #3
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I'm not sure if this helps much....but...I've been having battery issues and purchased a new DieHard battery that's currently sitting on my 2009 E93's floorboard. It's also an H8 AGM and is marked with the same 900 CCA's....160 reserve capacity, but is also marked with 95AH. I purchased the Bimmergeeks protool coding license but am stuck waiting on the arrival of the bluetooth adapter. Waiting to install it until that comes later this week. I think your 96AH is dang close and I'd imagine your battery is the same internally as mine and is probably the same 95Ah as mine is marked. I'm not a battery guy and am just guessing though!
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      09-16-2020, 05:13 PM   #4
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....and from everything I've read while researching my battery issues and coding it seems as though going lower is better then going higher if things aren't 100% known. Meaning don't go with that 100Ah you were talking about.
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      09-16-2020, 07:17 PM   #5
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Quote:
Originally Posted by fgpalmer71 View Post
I'm not sure if this helps much....but...I've been having battery issues and purchased a new DieHard battery that's currently sitting on my 2009 E93's floorboard. It's also an H8 AGM and is marked with the same 900 CCA's....160 reserve capacity, but is also marked with 95AH. I purchased the Bimmergeeks protool coding license but am stuck waiting on the arrival of the bluetooth adapter. Waiting to install it until that comes later this week. I think your 96AH is dang close and I'd imagine your battery is the same internally as mine and is probably the same 95Ah as mine is marked. I'm not a battery guy and am just guessing though!

Thanks. Very frustrating the a Champion rep would tell me 125 and potentially be off by that much.
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      09-16-2020, 07:19 PM   #6
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Quote:
Originally Posted by Emilime75 View Post
Calculating AH from RC is really not possible. They are measured differently, using different loads and methods.
There are generalizations, what you're finding from the "calculators" and "formulas", but those are just best guesses.
Some say divide RC by half, some say divide by half and add 16...you can see why this is a problem. It looks like your 96AH rating was concluded by dividing RC in half and adding 16?

If the battery manufacturer hasn't tested for AH and made that info available, somewhere, then the only way for you to truly know is to perform some testing on your own.
Correct on the way I got 96. I will forward your thoughts to Champion and see what they say.
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      09-17-2020, 09:46 PM   #7
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Woo Hoo!! From Champion. Battery specifications!

Not sure but these might apply to other batteries manufactured by Johnson Controls.
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      09-18-2020, 08:15 AM   #8
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I figured it would be identical to the specs marked on my battery! Good deal.
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