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Voltage drop key on #772925
05/07/19 6:09 pm
05/07/19 6:09 pm
Joined: Oct 2017
Posts: 221
MA
N
Nick H Offline OP
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Nick H  Offline OP
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Joined: Oct 2017
Posts: 221
MA
My 12 volt battery is fine with no load. Reads 12.8 or even 13 when charged. When i turn the key on it drops to around 10 volts. A tail light and points are the only things in the circuit. If I disconnect the points, the voltage goes back up.
Do I have a bad battery?


1966 BSA Lightning
1967 Triumph "Choppa"
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Re: Voltage drop key on [Re: Nick H] #772930
05/07/19 7:19 pm
05/07/19 7:19 pm
Joined: May 2013
Posts: 5,560
West Yorkshire
Allan Gill Online happy

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Allan Gill  Online Happy

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Joined: May 2013
Posts: 5,560
West Yorkshire
Yup!


beerchug
Re: Voltage drop key on [Re: Nick H] #772973
05/07/19 11:45 pm
05/07/19 11:45 pm
Joined: Oct 2017
Posts: 221
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Nick H Offline OP
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Nick H  Offline OP
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Joined: Oct 2017
Posts: 221
MA
Thanks. They don't last long do they?


1966 BSA Lightning
1967 Triumph "Choppa"
Re: Voltage drop key on [Re: Nick H] #773005
05/08/19 6:25 am
05/08/19 6:25 am
Joined: May 2013
Posts: 5,560
West Yorkshire
Allan Gill Online happy

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Allan Gill  Online Happy

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Joined: May 2013
Posts: 5,560
West Yorkshire
If your not using the bike regular no, they don’t and it’s important to keep them charged up. Once they have failed it’s usually the end for most batteries. The other thing is if the charging system on the bike isn’t getting the battery up to full capacity then this will also shorten the life. But crucially, disconnect the battery and put it on charge soon as it’s not in use. They can then last a very long time, it only if the battery is at full charge.

Is it a dry cell (AGM), or traditional lead acid?
(Both above are similar but AGM has matting between the plates and are totally sealed, unlike the traditional battery where you can top them up.

Gel is different again and most people who think they have a Gel battery... often dont


beerchug
Re: Voltage drop key on [Re: Nick H] #773311
05/11/19 1:17 am
05/11/19 1:17 am
Joined: Jan 2018
Posts: 18
Arizona Territory
S
Sinical Offline
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Sinical  Offline
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Joined: Jan 2018
Posts: 18
Arizona Territory
A standing charge of 12.8V with the bike not running is very good. After turning only the key on, it's normal for a gradual voltage drop, sometimes dropping to 11V or even 10V. If it's not dropping below 10V with key on, I wouldn't condemn the battery based on that alone.

Once the voltage drop stops and you turn the key off again, does the voltage return to 12.8V ? Does the bike fire-up without any problem ? Once running, does it idle at between 13.5V - 14.5V ?


1966 TR6R (stock)
1970 TR6R (chopped)
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