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Thread: Battery tending

  1. #1
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    Battery tending

    In 26 days the 8 will be going to sleep for 4-5 months. Can someone please tell me what the best method is for taking care of the batteries during this time. I have read 3 different opinions on the matter. Battery tender on points under the hood. Battery tender on the passengers side battery in the trunk and finally remove them from the car and hood up separately.
    The car will not be started at anytime during the storage period and yes it will be kept in a climate controlled garage.

    I'm leaning towards taking them out of the car.

    Thanks in advance for your advise.
    2015 F80 ///M3 Alpine White / Black
    2011 E93 ///M3 Space Grey Metallic / Fuchsrot
    2004 E46 ///M3 Laguna Seca Blue / Black
    1997 840Ci Jet Black / Black

  2. #2
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    Battery tender to power connection under hood or cigarette lighter. I do/prefer the latter. No need to remove. More work and the car will lose all memory functions unnecessarily.

  3. #3
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    I miss my E31!!!!!!!!!!
    I don't like to keep the tender on for that long of a time. It will be OK if you take it out for a spin every 4~6 weeks. Otherwise I recommend writing down the radio code and disconnect the batteries completely. This will prevent any accidental overcharging and/or boilover.

    YMMV

  4. #4
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    I use two CTEK 7002 chargers, take both batteries out and leave them on normal (or snowflake mode if during winter) for weeks at a time each year, the charger brings them to 100% and sustains them there, the batteries will never get overcharged and can only be strengthened by the CTEK charging system. I'm going on year 5 with my batteries with perfect function.
    Mīka / 1991 BMW 850i / ZF4HP24 E/H

  5. #5
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    4 or 5 months is not a lot of time. I connect mine to a trickle charger from November - May. If the weather is nice I will take it out as long as it's dry. I guess the question is will you be able to keep an eye on the car while it's stored? Even though battery tenders are normally safe. I wouldn't want to leave mine completely unattended. If leaving the car unattended I would pull the batteries and put each on it's own tender.
    Last edited by toomann; 11-06-2013 at 05:46 PM.

  6. #6
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    Quote Originally Posted by toomann View Post
    4 or 5 months is not a lot of time. I connect mine to a trickle charger from November - May. If the weather is nice I will take it out as long as it's dry. I guess the question is will you be able to keep an eye on the car while it's stored? Even though battery tenders are normally safe. I wouldn't want to leave mine completely unattended. If leaving the car unattended I would pull the batteries and put each on it's own tender.
    I can see the car every day it's stored if I wish. It looks like I will be leaving the batteries in the car while stored for the winter.

  7. #7
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    Quote Originally Posted by toomann View Post
    4 or 5 months is not a lot of time. I connect mine to a trickle charger from November - May. If the weather is nice I will take it out as long as it's dry.
    Same here. 1 battery tender, connected under the hood.

  8. #8
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    Battery tenders under the hood on two cars for months at a time - never had a problem.

  9. #9
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    You might find this of some use. I've put a link below that talks about connecting the "Battery Tender" to various battery configurations. I connected mine following figure 9 in this link (two batteries in parallel). Even though it's a max of, I think, 1.25 amps I hooked it with the "blue" wire in figure 9; also I replaced the clamps with ring connectors so it's easy to just remove the tender when needed. I've only had my 8 since Feb of this year but it could only go about three weeks of sitting before wearing down. Now with tender I've not had that problem. I have had good luck with the tender on my E24; using the same one since '05. Anyway here's the link:

    http://batterytender.com/resources/c...s-chargers.htm

  10. #10
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    I use one from Deltran also. The waterproof one. Connected under the hood.
    95 840Ci, Calypso Red/Silver, 83k - 99 740i, Black/Black, 185k, Alpina Mods - 01 740i, Titanium/Silver, 40k, Sport Pkg
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  11. #11
    tvjake2's Avatar
    tvjake2 is offline SoCalEights - CA BMW CCA Member
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    I dont have this issue (California) but a fellow 8er uses a timer on his trickle tender. Runs it 4 hours per day. He's never had issues.

  12. #12
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    I keep my car on a tender all of the time other than when I drive it of course. I keep it in storage all of the time as I don't have room to keep it at home. I got this tender at the dealer for $70.00 and haven't had any issues in the 2 years that I've had it. I drive my car anywhere from once a week to once every couple of months.
    FYI- This plugs into the cigarette lighter.
    Last edited by rharris99; 11-07-2013 at 10:51 PM.

  13. #13
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    Quote Originally Posted by mjrgroup View Post
    the charger brings them to 100% and sustains them there, the batteries will never get overcharged and can only be strengthened by the CTEK charging system.
    +1 for CTEK. They have this issue licked. Engine bay for me.

  14. #14
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    I use the CTEK ones, for long term storage I always disconnect the batteries and run one CTEK 3300 per battery. For short stints I usually just run one CTEK 7002 to the under hood terminals and let it do its thing. I really don't know which method is best, I just know its worked out well for me in the past.

  15. #15
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    Ctek

  16. #16
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    Quote Originally Posted by Winks View Post
    I use the CTEK ones, for long term storage I always disconnect the batteries and run one CTEK 3300 per battery. For short stints I usually just run one CTEK 7002 to the under hood terminals and let it do its thing. I really don't know which method is best, I just know its worked out well for me in the past.
    If you are running two batteries in parallel (stock e31) then you need to add up the total capacity (aH) and make sure the 7002 can support that. For example, I'm running two Duralast 49DL batteries, each with 155aH of capacity for a grand total of 310aH. One CTEK 7002 is not sufficient! If you want to run ONE CTEK charger to charge both in parallel then you'll need the CTEK 25000 ($250). The CTEK sees a parallel setup of batteries as a single large battery. The CTEK 25000 supports aH configurations of up to 500.
    Mīka / 1991 BMW 850i / ZF4HP24 E/H

  17. #17
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    I was using a C-Tek 3300 and it seemed too hot charging both batteries so now I use it on one battery at a time. I need the alarm on at all times so I remove the negative cable at the back left of the trunk. That takes 30 seconds. Takes less than 24 hours to fully charge each battery and then I don't recharge the battery for another month. Even though the batteries are now old maybe 5 years OEMs the car can sit for 3 weeks and still start, not that well, and that is with original GMs.
    Last edited by llcarlos; 01-24-2014 at 04:19 PM.

  18. #18
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    If you take the batteries out then,apart from radio code,make sure you are familiar with the boot [trunk] opening procedure in advance on an E31 with no power source.Timm`s site has the procedure.It is just a heart-stopper if you are not prepared for it when you try to re-fit the batteries.

  19. #19
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    Maleficent is living on a new CTEK Multi US 4.3, I have it hooked up via the alligator clips on the passenger side battery. Seems to be doing fine. I was concerned about over heating but if you have to worry about over heating with both batteries you have something else going on in your electrical system. Mines cool to the touch.

  20. #20
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    Quote Originally Posted by mjrgroup View Post
    If you are running two batteries in parallel (stock e31) then you need to add up the total capacity (aH) and make sure the 7002 can support that. For example, I'm running two Duralast 49DL batteries, each with 155aH of capacity for a grand total of 310aH. One CTEK 7002 is not sufficient! If you want to run ONE CTEK charger to charge both in parallel then you'll need the CTEK 25000 ($250). The CTEK sees a parallel setup of batteries as a single large battery. The CTEK 25000 supports aH configurations of up to 500.
    You make a mistake: The Duralast 49DL is not 155 Ah. In fact I can't even find the Ah rating. It's listed as 155 reserve minutes. I've never seen battery capacity expressed like that here in Europe so I'm not sure what exactly it translates to, but comparing to other batteries that list both reserve minutes and Ah it should be around 85 - 95 Ah what makes sense given the dimensions of the batteries.

    The CTEK Multi 7002 is capable of charging batteries between 14 and 150 Ah, but it can maintain batteries up to 225 Ah. So even with a pair of Duralast 49DL (170 - 190 Ah) it's well within specs for maintenance. Only if you cannot maintain the batteries (no power outlet near the car for example) and have to charge the (partially depleted batteries) every once in a while, you may have to look at a more powerful charger like the CTEK Multi 25000 (even though the 7002 will probably charge them as well - it's just going to take a lot longer).

  21. #21
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    Batteries that have more than 100Ah can't phisicaly fit in the battery tray, at least not in the one on the drivers side without removing the car lift bracket.
    I have used ctek 7002 for charging and mantaining 2x100Ah batteries in this car without a problem, but the batteries were never below 12v
    Last edited by duje; 01-25-2014 at 09:59 AM.

  22. #22
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    Quote Originally Posted by tvjake2 View Post
    I dont have this issue (California) but a fellow 8er uses a timer on his trickle tender. Runs it 4 hours per day. He's never had issues.
    Gr8 tip! My Schumacher charger/maintainer doesn't shut down....it runs continuously, a timer should work fine.

  23. #23
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    Would $105 CDN be a good price for a C-Tek 7002? My 3300 was around $60 but we have to pay 13% for the USD exchange rate and 7% for duty.

  24. #24
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    Have separate "battery tenders plus" units on the 850 and the M6 side by side in the garage for weeks to months at a time year round. Hooked up under the hood to the charging posts. No issues on the 850 at all. The newer M6 gets a little persnickety with an occasional iDrive system warning upon start up about unusual battery drain the first time you start it but goes away with a shut down and restart. I assume that is something in the M computer telling it that the battery charging has been cycled while the car was sitting. Otherwise the units charge up to "green" (fully charged) and cycle to keep them there. Got them off of Amazon but lots of places sell the units.

  25. #25
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    Quote Originally Posted by llcarlos View Post
    Would $105 CDN be a good price for a C-Tek 7002? My 3300 was around $60 but we have to pay 13% for the USD exchange rate and 7% for duty.
    I had paid around $120 Canadian from a cteck dealer at a car part flea market for my 7002.

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