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  1. #1
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    Minimum batt voltage needed to start an e39?

    Ok, got a question. Will a battery that is only charged to 10.5 or 11 volts even start our cars? Is there a difference if that battery was trying to start an I6 vs a V8?

    Reason I ask, after getting home today I went out to start the car, and the car would barely even crank. I mean, it sounded like the battery was heading towards gone. I put the voltmeter on there, and it is only registering 10.9 to 11 volts. Is that enough to start our cars??

    I wonder if that battery got run down when I had it disconnected, working on the ZF transmission, and it sat out there for days not running while Belgium has had baking temps between 75-80 F. I stupidly did not replace it last winter before last (had fixed a parasitic battery drain via replacing the FSU) because honestly I forgot about it after fixing that FSU. The battery is a good 8 years now, and I am going to reaplce it now no matter what.

    Still, my question stills stands: is 10.9 to 11 volts enough to start our cars? If that is still plenty to start the car, then I've got to check other issues. If not, I won't worry and will wait until I can get a new Interstate MT-49 battery here on our military base exchange store.

    Thanks for any replies!
    EuroDavid
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  2. #2
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    That's the surface charge you are reading. The battery needs to have some type of a load on it, 5-10 amps, to drain off the surface charge to read the true voltage. The V8 takes more current to spin the engine that an I6.
    If you were reading 11 volts with the headlights on it probably would start. Try measureing the voltage while you are cranking it, bet it drops down to 8-9 volts. Time for a new battery.
    Last week I found a Battery Tender Jr. on sale and snapped it up even though I have a 2/10/50 amp charger.
    Just a few mods.
    If it ain't broken make it better and quicker!
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  3. #3
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    Aw, ok, forgot about it having to be running while I did that voltmeter thing (haha....damm electrical stuff). I'll have to wait for the wife to come home so she can crank it with the lights on and then I do the voltmeter thing.

    I just called out at our base exchange store, they have a new Interstate Mega-tron 93 (MTP-93), 1000 Amps, 1000 Cranking Amps, 850 Cold Cranking Amps, 12 volts, and it is the one specified by Interstate for our e39s. They said it is only $85? I said "sold". I thought those batteries were like $135-$160 new??

    Either way, a new battery is going in. Before I forget, another question: should I trickle charge this new Interstate battery overnight (out of the car) before dropping it into the car tomorrow?



    P.S. One of these days when I come back to the States, I am going to pick up one of those Battery Tender Jrs. I've been meaning to for over a year now, when I see them online for sale. Can't find them over here, and it is an item that causes problems shipping (why, I don't know?)
    EuroDavid
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  4. #4
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    The headlights being on was just to remove the surface charge. If you are going to measure the voltage while cranking you don't need to have the lights on, the starter will be a big enough load on the battery. You must have some clip leads so you could connect the meter to the battery post under the hood??
    Excellent price on the battery, must be the PX discount. It wouldn't hurt to charge is before using it. I think I'd put in on a regular charge setting (~10 amps) for 30 min or so to see how long it take before the charger current starts to drop down, then switch it to trickle charge overnight.
    Just a few mods.
    If it ain't broken make it better and quicker!
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  5. #5
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    probably cheaper as you are buying from the PX. I wonder how fresh battery is as it must come from US. But if it works who cares. It is a favorite State side battery for e-39s make sure you get the vent kit. I 'm sure you already know that oh Wonderful transmission guru.
    2000 528 5sp Premium Package. Titanium silver,grey leather, heated seats,folding seats, 6cd player, bone stock except ash tray mod. Garmin GPS
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  6. #6
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    I had two MTP-93s and both of them were able to spill electrolyte around the trunk of my E39. MTP-93s require a cheesy press-fit vent kit and both of mine (purchased years apart in different cities) were overfilled from the factory. The MT-49s (or any other group 49) will use all of the original style plumbing for the vent which uses the barbed elbow in the end. Additionally all other group 49 batteries I saw when doing my research had individual threaded cell caps with O-rings. The MTP-93 has a crappy plastic snap-in affair with no rubber involved. I would get crystal growth all around those vents even though my system wasn't overcharging.

    I have pics.

    If it's not to late, get a 49.
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  7. #7
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    I just got back from driving out the military base and back. It's 10pm, my old arse should be in bed. Was expecting to see the supposed MTP-93, and it really is a MT-93 (person helping on the phone got a little mixed up when I was asking). Anyhow, guess what? The MT-93 is really the MT-49! I looked at it and it looks identical to the MT-49 I saw on the web? Same color, the vent opening is oval on the top of the middle of the battery, and it only has 750 CCA (unlike the 850 CCA on the MTP-93)? Same everything as the MT-49.

    Did I get lucky, Craig, based on what you said?? Even now I am sitting here looking at pics on the web of the "MT-49" and it is identical to the MT-93 in front of me. In fact, I cannot find a MT-93 labelled for you guys over there, so Interstate must have re-labelled their MT-49 as a MT-93 for the military. Hope I got lucky, and don't have the headaches Craig mentioned.



    p.s. I checked the date stamped on it, and Interstate charged it at the factory in Jan of 2011. Within the 6 mo window, yes? But it had no vent kit, but thankfully I stole two off Interstate batteries from the Autozone store last time I was home (with approval of the guys working there, of course).


    UPDATE AFTER POSTING----- it is official: Interstate re-labels their MT-49 battery as MT-93 for U.S. Military personnel around the world.
    Last edited by eurodavid; 04-26-2011 at 04:34 PM. Reason: update
    EuroDavid
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  8. #8
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    The real issue with old batteries is not terminal voltage, but internal resistance. As a battery ages,the resistance goes up, until it cannot deliver much current. This is the result of sulfation of the plates. The process is accelerated by allowing a dead, or partially charged, battery set around for a long period of time.

    I always charge a new battery overnight before installing. I have a smart charger that starts out at 6A, and tapers down to float.

    BTW, the electronics in our cars get funky when the battery voltage drops to the 10V region, and all sorts of funnies occur.
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  9. #9
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    If it's like below, you are not lucky. I had two do very similar things despite different years of manufacture and city of purchase. The first one puked enough acid in the trunk to run down into the spare tire well and pool before drying. I needed to have the anti-rumble stuff pulled and the whole thing cleaned, primed and painted.

    These are pics from earlier this year a couple of months after I cleaned everything up and tried foil+clear duct tape to try to seal vapors and little acid spittle inside to no avail. My charging voltage is <14VDC, so it's not an overcharging problem.

    click here

    You can see the cheesy vent nipple near the R of INTERSTATE. You'll also notice the cells are overfilled, even after 5 years on the road. I have checked the level at least annually but never added any water.
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  10. #10
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    Yes | No
    Craig,

    Argh...! I am really confused---this is the battery i just bought:



    What I don't understand is that, if you look closely at pics of their MT-49 on the web, it is the exact same battery as we are looking at (including yours). Here's a web link pic of the Interstate MT-49:





    What the heck is the difference between that web link picture and the new battery I just bought (and for that matter, the pictures in your link)? The only thing different I can see is that I have a handle, as does the web pic, but you don't (I imagine you removed it to be better get at cleaning the puking stuff). Everything else is the same, from vent hole, to fill holes, to dimensions, etc.

    What did you mean get their "49" series battery? This (yours, mine, the web pics) is their "49" series battery? Yes??

    Thanks for any replies.



    P.s. Anyone else have this battery and have the problems Craig had? I am reluctant now to put this in my car if it is going to puke all over. Belgian roads, as you all know from me talking about them, are not smooth and/or level in the southern half of the country. The battery has to be able to withstand the constant bumping, pot holes, uneven roads, etc.
    EuroDavid
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  11. #11
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    OK, MTP=MegaTronPlus, MT=Megatron. It's a warranty and CCA difference.

    Johnson Controls makes Interstate. They're the #1 battery manufacturer at the moment and make all kinds of brands, including Costco and Walmart's. A true group 49 has end venting and circular, screw-in caps with O-rings. More like this (chosen from the Internet at random):



    This time I've gone with an East Penn/Deka manufactured wet-cell. They also make a snazzy line of AGM (absorbed glass mat) batteries which have no liquid electrolyte and will never leak (but cost 2-4 times as much).

    Around here, the cheapest I found JCI-made group 49s was $117 or so at Walmart, but I know that they are quite a bit less in the US. At this point I feel that East Penn makes a better product that will hopefully keep all of its acid on the inside this time. Deka has a line of "Exact OE fit" batteries made for European vehicles. They offer the 649MF wet cell and 9AGM49 AGM battery to fit the E39. At 900CCA they also have 200CCA more than the original BMW battery (mine was 700CCA - maybe 750).

    See more here: http://www.dekabatteries.com/assets/base/0379.pdf
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  12. #12
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    Thanks, Craig.

    I didn't know the difference.
    EuroDavid
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