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Thread: Advice, Second Battery for R1150RT

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  1. #1
    Registered User jsoque's Avatar
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    Advice, Second Battery for R1150RT

    I've often wondered if I need a second battery in my '04 R1150RT for operation of my gadgets, and Gerbings heated clothing.

    Has anyone had any experience with wiring a second, 12 Volt, Lead Acid Sealed battery, into the 'Radio Compartment' box of an RT?

    I imagine that the hook up is in series, that is plus to plus, and minus to minus to the bikes main battery.

    Then there is the charging factor; and does my alternator charge this battery at the same time the bike is operating?

    (I can hear your thoughts now: Oh No, this guy's headed for trouble...)

    However, I would appreciate any input, as well as choices for a battery purchase of the many that are out there.

    As for the project, I'd imagine that it would involve me removing my L side tupperware, and running some heavy guage wire to the main battery, before I run some splits off for my GPS/Iphone charger/Gerbings heated clothing.

    Any advice is much appreciated,
    (and believe you me, I won't start this project without all of you involved, 'cuz Vince would kill me, and also, I don't want to come out to my garage, to a melted bike')

    Ride Safe, Stay Warm

    Jim
    on Long Island, NY
    '10 R1200RT - Ostra Grey
    '04 R1150RT - New Life in Upstate N.Y.
    '04 R1150R - New Life in Virginia

  2. #2
    neanderssance man sedanman's Avatar
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    "I imagine that the hook up is in series, that is plus to plus, and minus to minus to the bikes main battery."

    This is actually parallel and yes, that's how you would do it , stay at 12 volts and get double the amperage (assuming identical batteries). I think police bikes came this way.
    Paul
    "Friends don't let friends ride junk!"
    2011 R1200RT

  3. #3
    Benchwrenching PGlaves's Avatar
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    Some police bikes came with two batteries. That was so lights could flash a long time with the engine off. Most RVs have a similar setup - engine battery and one or more coach batteries.

    RV setups have either a relay isolator or a diode isolator so the alternator will charge the coach batteries but the lights, etc. won't drain down the engine battery. I don't know if the police bikes had that or not.

    That said, a second battery is not the answer to powering gizmos if you mean while you are riding. Not for very long at least. If the current draw from all of the devices plus the bike exceeds alternator output two batteries will just give you two discharged batteries instead of one.

    Now, the alternator really likes to see 2,000 or above rpm for peak output, so if you do a lot of putting around with starts and stops at low rpm the second battery would be a bigger reserve, but for most riding it wouldn't gain much of anything except add weight.

    Your R1150 should have a 700 watt alternator. On my R1150R that is sufficient to power two 55 watt driving lights, two 55 watt Motolights, my Gerbing heated jacket liner, the heated grips on high, and all bike house loads including high beam headlight. I don't even count the two GPS units and radar detector because those loads are miniscule.

    If you are having battery discharge issues it is because the battery is bad, the charging system has a defect, or you have a drain someplace unless you are riding around a lot at very low rpm.
    Last edited by PGlaves; 11-15-2012 at 11:11 PM.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  4. #4
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by PGlaves View Post
    ...

    That said, a second battery is not the answer to powering gizmos if you mean while you are riding. Not for very long at least. If the current draw from all of the devices plus the bike exceeds alternator output two batteries will just give you two discharged batteries instead of one.

    Now, the alternator really likes to see 2,000 or above rpm for peak output, so if you do a lot of putting around with starts and stops at low rpm the second battery would be a bigger reserve, but for most riding it wouldn't gain much of anything except add weight.

    ...
    +1 on the above. Also, for low RPM starting of the alternator, you should check that you have a 3W bulb in the Batt indicator lamp. Mine was only 1.7W and I accidentally discovered that BMW seemed to have changes the spec somewhere along the line.

    The best function of a second battery is that when installed in the left-side-of-tank storage compartment, its 14 lbs. weight better balances the motorcycle, eliminating a slight pull-to-the-right that most R1150RTs exhibit. I didn't realize mine did until someone pointed it out. That PTTR can be well mitigated by 12 lbs. of lead shot in the compartment which fits in the bottom inch of that box. You'd be surprised at the difference.

  5. #5
    Pepperfool GSAddict's Avatar
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    Quote Originally Posted by sedanman View Post
    "I imagine that the hook up is in series, that is plus to plus, and minus to minus to the bikes main battery."

    This is actually parallel and yes, that's how you would do it , stay at 12 volts and get double the amperage (assuming identical batteries). I think police bikes came this way.
    The police bikes have a Heavy Duty Relay isolating the two systems so Battery #2 may be discharged without affecting #1 when the bike is off.
    '
    Ufda happens..........

    It's all about the details.

  6. #6
    Registered User kioolt's Avatar
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    I really don't think you will discharge your single battery on an R1150RT with the normal amount of add on's that I have seen. If you are really worried about a dead battery I believe the way I would go would be to get the R1150RTP's 840 watt alternator and install it. It should be an easy drop in replacement. They show up on eBay ever so often. I thought about doing that but I have never had any problem with running 2 electric vests, heated grips, gps, satelite radio, intercom, extra low wattage lights, and a heated seat.
    2004 R1150RT 145,700 miles
    1991 K100LT 126,700 miles
    1982 R100RT 106,900 miles
    Total 379,300 BMW miles

  7. #7
    Registered User twinsig's Avatar
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    yes, over kill

    Your gizmos aren't drawing enough power to justify all the crap you would need to go through to add a battery.
    Democracy is two wolves and a lamb voting on what to have for lunch
    Liberty is a well-armed lamb contesting the vote

  8. #8
    Seattle-area Rounder OfficerImpersonator's Avatar
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    Two batteries = 2x the trouble

    I've put 56,250 miles on my RTP over the past five years, and at this point, I'll have to say having two batteries doesn't provide enough bang for the buck.

    The 2nd battery in the left-side glove box/radio box puts a big chunk of weight high up on the bike. The wiring to accommodate the 2nd battery adds unnecessary complexity to an already complicated wiring harness. Trouble-shooting electrical gremlins becomes more difficult with two batteries.

    I've often contemplated removing the 2nd battery from my RTP, and going with just the main battery under the tank.

    I'd recommend against it. Your RT's alternator and one battery can handle the lights and heated gear.
    Seattle, WA
    2012 R1200GSA
    2002 R1150RT-P
    1992 K75S sold

  9. #9
    Registered User
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    Yeah, that second battery is just there for the extra police equipment that may be on while the bike's ignition is off- emergency lights, radio, radar, so the main battery doesn't get drained and the bike starts after the motor vehicle stop or whatever the officer was on.

    As has been said, a single good battery and alternator will be able to power anything you can mount, within reason.

  10. #10
    Day Dreaming ... happy wanderer's Avatar
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    +1 on the previous comments. 700 Watts is plenty of power for heated grips, clothing and some other accessories. I've ridden with guys who can warm the back of my head up with the lights and gadgets all powered from a stock electrical system.

    Officer Impersonator mentioned the extra weight, wiring and maintenance associated with dual batteries and that alone is a good reason not to do it!

    That glove box is super handy on the road too.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  11. #11
    Alps Adventurer GlobalRider's Avatar
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    Quote Originally Posted by jsoque View Post
    I've often wondered if I need a second battery in my '04 R1150RT for operation of my gadgets, and Gerbings heated clothing.
    I can't see why you would need to unless you are powering all your gadgets with the engine off...or you are in "silent watch mode" off on the battle field.

    You have a 700 watt alternator that can keep up with your power draws.

  12. #12
    Registered User
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    Auxiliary Battery

    The auxiliary battery on my R1150RT was dead and drained the main battery.
    i'm taking it out and using the compartment for storage but can't get the battery strap unhooked. Looks like a bolt
    holding the strap but hard to see. Can anyone help?
    Peter.

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