brian5,

Can you do a write up and post a couple of pics when you do the battery registration using Tool32.

If you happen to do a coding as well, please include.

Thanx!

From the Interstate web-site, it appears that your MTP-49/H8 is a Wet Cell battery and only rated at CCA 720. I saw a MTP-49/H8 battery today that was Wet Cell and rated CCA 900 (with 79 Ah). So I think Interstate has a lot going on with their batteries (and using the same codes) that are adding confusion. So I don't know what yours is...

Based on the Interstate website, it looked like I wanted the MT5-49/H8 (which is AGM and CCA 900). Interstate says they don't sell that yet. The shop spoke to Interstate and is going to get me the MTP-49/H8-A (which is supposedly AGM and has CCA 900). I'll check it out before they install.

Actually found a PDF file that covering registration and coding batteries. You need to register batteries, for engines not covered in INPA, using Tool32. An example is our 4.8i aka N62 engine.

The "ah" values listed in the PDF are not applicable to our 2008 X5 4.8i. I had the correct list posted above which one can get from NCS Dummy.

brian5,

I've asked the SAME question: why do some battery manufacturers not list the Ah value?

The problem in understanding Ah arises when we speak about a battery of a given Ah capacity. If we have a battery rated at 100 Ah, that battery can supply 5 Amps of current for 20 hours. That same battery can't supply 100 Amps for 1 hour, however. In fact, it can only supply 100 Amps for about 1/2 an hour. Why?

The true capacity of a battery is dependent on the rate of discharge. The faster the rate of discharge, the less total Ah capacity can be delivered. This phenomenon was described mathematically back in 1897 by a researcher named Peukert. He formulated the equation:

I(exponent n)T=C

In Peukert's equation, the letter I is the discharge current, letter n is a value related to battery construction, letter T is the duration of discharge, and the letter C is the capacity removed as a result of that discharge. If exponent n is equal to one, then we have the familiar circumstance where 1 Amp for 100 hours is equal to 100 Ah. (I = 1, n = 1, T = 100, so C = 100 Ah.) But, exponent n is never equal to 1, even in the best of batteries. Exponent n has normal values of 1.05 to 2, with about 1.2 being a common value. Lets use n = 1.2 in Peukert's equation with I = 100 Amps. We now find that C = 251 Ah. In other words, if we want to draw 100 Amps for 1 hour, we need a battery of 251 Ah, assuming the battery has a Peukert's exponent n = 1.2. Suppose we have an exponent of 1.1. For 100 Amps, C now equals 159 Ah considerably lower than 251 Ah. As mentioned, exponent n is related to battery construction. The lower the value, the better the battery will supply high currents.

Note that for low values of current, the value of n doesn't have much impact on capacity C. As currents increase, however, the effect of n is significant.

What this demonstrates is the need to measure Ah using Peukert's equation if we really want to stop guessing about battery capacity.

For a battery with an exponent of 1.2, a 2 Amp draw for an hour actually removes 2.3 Amp hours, or about 13% more than a linear measurement indicates. A 20 Amp draw for an hour results in a depletion of 36.4 Ah ...a whopping 45% more than a linear measurement would show!

How accurate is Peukert's equation? Recent tests indicate that errors are in the range of 0.5-1%.

Given that these cars are designed by German engineers, it does not surprise me in the least that they want to make sure that the battery they specify must have the correct Ah value ...

In America it is much more effective to market the battery with Cold Cranking Capacity (CCA), because more must be better, right? However, the CCA value is only part of the equation and says nothing about the draw on the battery by our power hungry cars!

In order to list the Ah value on a battery, it must actually be measured, at least on a sample basis, on the production line ... who's got time for that?

Hope this helps.

OK

It would be interesting to hear Interstate's response.

East Penn Manufacturing, the manufacturer of the Duracell H8-AGM battery I was going to buy, simply said that the do not provide that information!

I wonder why ...

I thought a saw a way to calculate this. If I come across it I will let you know.

Interstate MTP-49/H8-A AGM, CCA 900, Ah 94: those values are a good match to the original equipment battery in our cars. The 94Ah rating could easily be close to the 90Ah value depending on how it was measured by the manufacturer ... As a matter of fact, BMW's replacement recommendation for our discontinued AGM battery is a 92Ah version. Apparently BMW also believes that it can't hurt to have a few extra amps to draw from ...

Let us know if you're going this route. You should be able to get away with registering the battery only, but if you decide to do the coding, please show us pictures of how you used the Tool32.

What price have you been quoted for this battery? Where?

Just bought it and had it installed... Interstate MTP-49/H8A. It is AGM, CCA 900 and the Ah is actually 95 so no coding needed by me. My KLASSE_BATTERIE value is currently "90ah_agm" so that's as close as I can get. I have just completed the registration using Tool32.

The MT5-49/H8 is the newer AGM model but that was not available from the local Interstate distributor yet. Interstate says this is 96AH.

Paid $200 for battery at Firestone Complete Auto Care. $88 for labor (which obviously could have done myself but I figured I was saving so much anyway :) )

Good deal! Thanks for sharing.

I just asked my local garage here who's familiar with BMWs about registering my battery and they can do it for $45, but they said the battery must be bought through a dealer. I can't recall exactly the reason he mentioned but it had to do with MY2008s and onward - their batteries use 4.8(something) and not 4.0(something). He said we can't and shouldn't go to Interstate directly for those.

Aside from the possibility that he's in bed with dealers (doubt it), could there be any truth to this? He has an E46 M3 and mentioned that he dealt with 4 battery replacements before realizing he couldn't get batteries from outside.