Battery?/Charging Problem?

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    I am not over impressed.

    I got my bike out today to go over a couple of things, and For some reason I thought id test my BRAND NEW!! Motobatt battery.

    Thinking I would find it at somewhere in the region of 12 volts!

    NO!! 10.7 is what it was at 😮

    This could have something to do with the starter not turning over?

    I have put the battery on charge and I will see if it charges up to 12 volts, I have a feeling it will!
    and I will find I have an electrical fault somewhere the bike has ridden 150 miles since I put the battery on and Everything works on the bike apart from the neutral light and the starter!

    So I hope I can track what this is because these motobatt batteries are meant to be good! But this one has run on the bike less than a week ago, but now is only showing 10.7v 😮 😳


    Hi Tango,

    that is not good !

    I could see from their website, that Motobatt is only offering yellow “Absorbed Glass Mat” batteries, known as AGM or also as VRLA (valve regulated lead acid) batteries.
    I am working on a professional basis with huge numbers of these kind of batteries and they are quite reliable.

    Largest installation I have supported so far was 32 tons of batteries only + additional stuff to make up a UPS (Uninterruptable Power Supply) for a datacenter 😉

    Either your charging system (in the bike) doesn’t work or there is something that deplets the battery or the battery itself is faulty => warranty ?

    Are you using an “old” standard battery charger or an advanced one, that is capable to charge this kind of batteries ?

    Battery recharge current should be 1,4 A (one tenth of capacity, which I expect to be at 14 Ah = stock) or less. It will take 10 h or more to recharge the battery.

    These batteries are made up of 6 cells, each cell has a constant load voltage of 2.27 V. Times 6 this should be 13,6 Volts right after charging, disconnected from charger.
    After 3 to 6 month of storage they should show approx 12,0V with no load applied.

    Never open the plugs of this kind of battery !
    There is no acid level to control or purified water to refill.
    If the battery plugs are removed at any time, the battery is destroyed !

    Ok, check charging system(s) first.
    When battery is fitted in your bike, you should see a raise from 12V nominal to approx 13,6 V when motor is running with approx 1.500 rpms.
    It may go up to 14,5 V at higher rpms but should always be lower than 16,0 V, which is bad enough !

    Short version of that story:
    If you can’t see any raise of battery voltage at any rpms (up to 5.000 rpm) the charging system needs to be checked.
    If battery voltage goes up and down within mentioned range and changes with rpms, it can be treated as working fine 🙂

    Ah, of course the low voltage of the battery causes the starter not to turn. Measuring the battery voltage, when pushing the starter button, it will go down, of course.
    It should be 6x 1,65V per cell, which means 9,9 V total hopefully.

    But your actual battery voltage should be sufficient to get the starter relais / solenoid activated and to hear at least a “click” from it. Next try should have at least a “click” as a result, even if starter motor doesn’t spin.

    Let me know the result of your investigations 😉

    Cheers, Michael


    Hi Tango,

    forgot one thing.
    Each of the six (6) cells (nominal 2,0V) may be considered as faulty.

    If that happens (and it happens sometimes!) the nominal voltage is reduced to 10 V. After charging with external charger was done, this defective cell is not charged and the reading of battery voltage would be only 5x 2,27V = 11,3 V. Measured right after charging, but charger disconnected.

    Ok, measuring battery voltage right after charging is a dynamic process over some time, but battery voltage should be stable after some time (several minutes, max. one hour)

    Please let me know 😉

    Cheers, Michael


    No increase in volts on increased revs. The battery shows 11.4 volts now ive had it on a Datatool Bike Charger for a couple of hours!
    And no drop when I press the starter! Button with the motor stopped ?


    So will the bike be creating its own power to run
    So this is why I have had no issue when I’ve been riding it?

    I would never have known I had an issue if I had not of tested the battery by chance?


    Hi Tango,

    might be a double or even triple fault !

    Voltage after charging is as low as mentioned if a single cell fails.
    => warranty !

    No increase in voltage with raising rpms shows no charging by the rectifier / regulator.

    No drop in voltage when starter button is pressed shows a not working starter. Ok, that is nothing new to you 🙂

    Does the starter relais “click” ?

    How did you connect the “MINUS” of the battery?
    Original it is directly connected with a large (black) cable to right hand side of the motor, using a M6 screw, right above kickstarter and adjacent motor holder.

    Is that fitted firmly ?
    Had some trouble with a loose connection there !

    Cheers, Michael

    PS: Battery voltage after charging is to low ! Battery still has warranty ?


    Hi Tango,

    not sure about the points ignition ?
    May work even if battery voltage is low 🙂

    Contactless ignition of B3 and later will let you down if there is not sufficient battery voltage !

    Turning the lights off in such a moment is a help, but will last for only 50 or maybe 100 km.

    Using the winker (or the horn) and in same rythm motor stops working reminds you, that ignition is running on battery only 😉

    Does the starter relais click ?

    Cheers, Michael


    As Michael said if you have no voltage increase when the bike is running and revving above 1500 rpm, there is a charging fault and just running the bike will slowly drain it. Check the earth lead (negative battery lead) and check the connections to the rectifier and voltage regulator.
    You can also check voltages at the 3 yellow wires from the 3 phases of the alternator, and these are prone to corrosion in the multiplug connector.
    Points only systems will keep running at even very low voltages, down to 6 volts but you will get misfires as the battery gets lower.

    Battery chargers with low outputs will take a long time to recharge your battery, on a twin I believe it would be 14AH (14 amp hour) battery so if your charger only outputs 500 ma (1/2 an amp) it will take around 28 hours to charge your battery back up fully. Voltages are an easy way to measure batteries, but not the most reliable method (as a forklift truck engineer working on battery powered trucks this is something I have a fairly good knowledge of).

    You need to do one thing at a time, as your battery seems to be dropping off, that needs to be corrected before worrying about electric starters which will drain a battery very quickly (they can draw 100’s of amps so as an example a 14 A/H battery being asked to supply 280 amps will be dead in 3 minutes). So before anything else you need a good battery and charge system, bearing in mind lights, indicators, stop lights, running the coil for ignition etc. all take power which the battery won’t keep up with unless you have a good charge system to keep the power flowing.

    Another thing to bear in mind is if you use the bike for a short journey and park it up, and then another journey and another rest, the battery will pick up a little as it stands (to a certain extent anyway) and can make it seem as if the battery and charge circuits are OK for a while, so your 150 miles if done in one go would kill a battery if it’s not charging but a few trips with rests will allow it to recover slightly each time.


    Well I have had to do something I was going to leave for now!

    But I have dropped the oil.


    Cheers for all the help Guys 🙂

    I am going to need all the help I can get on this.
    I do not have any idea when it comes to Electrics? and this could end my trip before it even starts! 😕

    I know dropping the oil is probably not going to help much? But I want to see what’s going on under that side case? I want to make sure that everything is ok behind the cover before I start chasing wires at the top!

    Does the front cover come off without having to take the rear part that covers the front sprocket off?


    Another Worry I have is there has been some changing of wires up at the Regulator and the Rectifier?

    On my bike I do not have a finned block that I would know as a Reg/Rectifier Unit, It is two separate units!



    I put a lead off the – negative terminal straight to the frame and I made sure it was clean metal on the frame.
    And the starter relay does not even click?
    I did put the volt meter on the two posts on the solenoid and it showed me the same volts as the battery was showing.



    I only have a Datatool Charger?

    So I have put the Battery on charge now so it can trickle charge over a couple of days.

    So with a bit of luck that will put a good charge into the battery.


    Hi Tango,

    having two separate “boxes” for regulator and rectifier is a speciality of the B1 and B2 models, so that is correct.

    Having non-isolated plug connectors within the battery charging circuit causes goose flesh to me !!!

    Connecting the MINUS to the frame is ok, but source of electrical energy is the alternator in the motor casing. In the end there must be a good electrical connection also from the frame to the motor casing.

    Not sure if the cables connected to the 3-way plug needs a special order or can be plugged in anywhere?

    Attached two pictures of the Z750B2 electric as I just bought it.

    Cheers, Michael


    Hi Tango.

    you have to remove switch lever, right hand side foot peg and sprocket cover first, before you can remove the alternator cover.
    No other way possible.

    But leave that cover on.
    Apart from some coils you will not find the electrical power in there 🙂

    You can do some measurements on resistance of the coils. For that it is not needed to disassamble the cover.

    Will have a look if I can find some data for resistance measurements.

    Cheers, Michael

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