Before I fry the electronics...

Discussion in 'GS Boxers' started by Superfly, Dec 12, 2020.

  1. Superfly

    Superfly Redleg Supporter

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    ...do I have to buy the BMW battery charger that plugs into the accessory port, or can I use a battery tender from Walmart? The manual makes it seem as if anything other than the $200 DIN CAN-BUS charger will fry your bike.

    The $50 1.25 Amp Battery Tender from Walmart has been all I've ever needed to keep my non-BMW bikes and Yamaha outboard engines topped off.

    Appreciate the feedback!

    2019 R1250GSA
    #1
  2. GSBruce

    GSBruce Been here awhile

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    Wire an SAE-plug/pigtail directly to your battery. Use your Battery Tender.
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  3. bikermd

    bikermd Been here awhile

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    You need a battery charger/tender that is designed for AGM batteries and there higher voltage needs. I believe they like at least 2 amps of charge. You do not need the BMW charger. I have never used it but do use a tender designed for AGM batteries. My older tenders will not work.
    #3
  4. GS Addict

    GS Addict Pepperfool Supporter

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    +1
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  5. NoiZboy

    NoiZboy Dirt to Track and Back Again

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    Agreed. I've never used the fiddly, overpriced BMW charger and never had an issue. My one friend who was gulled into buying one ended up needing to borrow my Battery Tender when his BMW Charger stopped working due to some CANBus issue.

    If you have AGM, for ideal charging you need a stronger charger than a Battery Tender, but I've never used anything except a Battery Tender and I've never had an issue. Even the 5+ year old Odyssey in my R80ST has never been a problem and it's only ever seen a Battery Tender.
    #5
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  6. Superfly

    Superfly Redleg Supporter

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    Thanks, fellas.
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  7. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

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    Spot on!! :deal

    Added benefit of having SAE piggytail hard-wired to the battery is to use it, with an matching SAE extension cord, for powering anything else you may need to (air pump, or USB charger etc)... :thumb
    #7
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  8. vagueout

    vagueout Long timer

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    Likewise both my cam head bikes I fitted a Hella type plug with fuse direct to battery so if any of the cheap arse appliances I plug in, air compressor, battery tender ,whatever blow up ,the holy can bus is clear of the destruction.:*sip*
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  9. scottdc

    scottdc Been here awhile

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    I asked my dealer if the BMW charger was any good and he said "buy a cheap Battery Tender from Amazon". I mean if my dealer won't take my money it must be pretty bad! :lol3
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  10. tzracer

    tzracer Been here awhile Supporter

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    Make sure your charger does not go over 14.5 to 15V. Any higher can destroy the ECU.
    #10
  11. JimVonBaden

    JimVonBaden "Cool" Aid! Supporter

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    ??? Connected directly to the battery?
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  12. GS Addict

    GS Addict Pepperfool Supporter

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    Actually, the Motronic on earlier bikes is protected to spikes of up to 40V.
    I would expect no less of later models.
    These are typical design parameters for ECU's.
    It is to allow for high voltages created by the alternator when battery terminals loosen.

    Edit: I missed that this is a wet head. Shunt type regulator.
    Above applies to Oilheads and earlier.
    #12
  13. tzracer

    tzracer Been here awhile Supporter

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    Unless you remove a cable. Otherwise the ecu will see the charger voltage. Don’t want to get up and look in my manual, but I have seen warnings.
    #13
  14. JimVonBaden

    JimVonBaden "Cool" Aid! Supporter

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    Only if the battery lets it get charged that high. Note what @GS Addict said also. I have never seen this happen, ever.
    #14
  15. tzracer

    tzracer Been here awhile Supporter

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    You may want to go over to sport touring forum and read dirtrider reply’s about charging a wet head. He specifically warns about exceeding 15V. From one of his posts:

    BMW specifically cautions against exceeding 15 volts during charging if the battery is still connected to the vehicles electrical system to avoid possible system damage.


    My manual warns about using a non BMW approved charger directly to battery or through power port. Damage to port and electronics may result.
    #15
  16. JimVonBaden

    JimVonBaden "Cool" Aid! Supporter

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    And yet, sales attempt by BMW aside, I have still never seen an issue like that.
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  17. tzracer

    tzracer Been here awhile Supporter

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    It could if it goes into a desulfation mode, these can run at 20V.
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  18. JimVonBaden

    JimVonBaden "Cool" Aid! Supporter

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    OK, you win.
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  19. Prunelles

    Prunelles Adventurer

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    I run a Ctek MXS 5.0 battery charger with Ctek proprietary Eyelet battery cable. Ctek also offer a plug-in DIN cable “Cig Plug”.

    But Ctek said that the DIN plug must be “energized” to work !?
    #19
  20. bikermd

    bikermd Been here awhile

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    I have tested batteries for capacity after charging with various chargers and was surprised to see a significant difference when using a proper AGM charger. Both look charged but testing shows you are not near capacity when using a non AGM charger. If the battery has been only charged for a prolonged period with a non-AGM charger it can be impossible to get them back to where they should be. At the least it can take several charges before they will again hold a proper charge.
    #20