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Battery voltage drop


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Michigan boarder

On 6/29/21 I bought a Sam's Club Duracel 31DC since it still fits the battery box and has a lot more reserve amps than the 27DC's that I usually run.  We ran the boat for a while last night and when I put it away it read 12.81v with a multimeter.  Today when I checked it my reading was 12.71v.  Is that normal?

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Probably a surface charge that dissipated overnight. 12.7 sounds healthy to me. 

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Michigan boarder
19 minutes ago, drh said:

Probably a surface charge that dissipated overnight. 12.7 sounds healthy to me. 

That's what I'm thinking too.  It's kinda crappy outside right now so we probably won't use it, and if so I'll check it again tomorrow.

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Michigan boarder

I did check my alternator and am wondering if this is normal.  I have 4 wires on the alternator:

  1. One black wire which is ground, obvious one
  2. One orange wire that is about a 4 guage with a boot on it.  Also obvious, I'm sure this goes to the battery.  This wire measures 12.7 volts without the key in the ignition and nothing on.
  3. Two 16 guage wires
    • One wire is red.  It is connected to the S terminal.  This also measures 12.7 volts without the key in the ignition and nothing on.  I thought the "S" was for stator and that it would only measure voltage when the engine is running and the alternating is putting out voltage.  Am I wrong?  I've had it wired this way since I bought the boat.
    • One is purple.  It is connected to another terminal directly across from the red wire.  It has zero voltage unless the key is on.  I have wired my electric choke to this terminal.

Are those two smaller wires (and my choke) connected like they should be?  Last year I ran the electric choke from the coil, but I read that it's a bad idea to do that so made a change this year to connect it to the alternator.

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Purple wire should be ignition-on power.  In my setup, that wire provides the reference voltage from the dash.

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Posted (edited)

Resting voltage for a fully charged lead acid battery is 12.6.  This should be read after the battery has rested from discharge or charging for an hour or so.

https://www.google.com/imgres?imgurl=https://www.rvtechlibrary.com/images/voltchart.gif&imgrefurl=https://www.rvtechlibrary.com/battery/bat_volts.php&docid=13DVgjzf-kLFbM&tbnid=O1nPMjMeB3PBBM&vet=1&w=329&h=344&hl=en&source=sh/x/im

Edited by dlb
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