Battery voltage

MaxxdSVT

Active Member
Established Member
Joined
Nov 27, 2016
Messages
167
For past few months been noticing my battery voltage dip to as low as 12.8-13.2 range. When I start and drive it stays at around 14 but gradually declines as I drive. I don't drive the car much and it stays connected to a battery tender at all times in the garage. Would this be a battery or alternator issue? Haven't seen it dip below that but I'm worried it'll leave me stranded.

Sent from my SM-G960U using the svtperformance.com mobile app
 

shznit

shznit
Established Member
Joined
May 2, 2005
Messages
363
Location
Renton, WA
When I'm monitoring mine with my X4 I notice similar voltages... low to mid 13v. I'm only on my 2nd alternator since 2005 though (new, replacement). I'm keeping an eye on mine and if any issues develop going to replace/upgrade with J2Fab or Ken Miley Jr.
 

hotcobra03

Well-Known Member
Established Member
Joined
Mar 11, 2007
Messages
7,461
Location
poteet,texas
For me. The ground from battery to radiator support

Isn’t big enough and burnt inside.

I replaced it with a large cable pre made.

I always seen more volts at battery vs
Inside car.

Now I see the same.
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,913
Location
Central Fl
short of doing the ground upgrade I would check the battery directly with a volt meter and compare against the gauge - via the OBD2 usually shows at least .3 volts less than at the battery, some have a bigger delta. Id keep an eye on it and make sure it doesnt continue to drop though. The problem is far more likely the alternator if it continues to slide. You want to have at least 13V @ WOT to ensure fuel pump flow
 

MaxxdSVT

Active Member
Established Member
Joined
Nov 27, 2016
Messages
167
That's funny u say that about fuel pump flow. The other day my fuel rail pressure sensor took a dump on me on a wot pull on the highway. Maybe it was because of the voltage? This is still my factory alternator.
 

BlksvtCobra01

Deplorable and Proud
Established Member
Joined
Apr 10, 2008
Messages
13,555
Location
Ohio
short of doing the ground upgrade I would check the battery directly with a volt meter and compare against the gauge - via the OBD2 usually shows at least .3 volts less than at the battery, some have a bigger delta. Id keep an eye on it and make sure it doesnt continue to drop though. The problem is far more likely the alternator if it continues to slide. You want to have at least 13V @ WOT to ensure fuel pump flow

Where can I find this ground upgrade? Mine has been doing the same starts at 14 on my aeroforce then at the end of my drive as low as 13.2. When I had the ac on max the other day it dipped to 12.8 a few times. I did look and mine has been replaced at one point it says remanufactured on the case. I’ll try the dvom on the battery next time.


Sent from my iPhone using Tapatalk
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,913
Location
Central Fl
Where can I find this ground upgrade? Mine has been doing the same starts at 14 on my aeroforce then at the end of my drive as low as 13.2. When I had the ac on max the other day it dipped to 12.8 a few times. I did look and mine has been replaced at one point it says remanufactured on the case. I’ll try the dvom on the battery next time.


Sent from my iPhone using Tapatalk

@hotcobra03 has mentioned a few times replacing one of the small grounds from battery to rad support and it making a difference. I haven't really looked at that part of the harness
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,128
Location
Cali
When I've had the issue of the volts dropping as things warmed up it was the alternator. The ground might be getting finicky if its corroded inside. But mine did it with an upgraded ground as well. I went with the J2 Fab when it was on sale.

You can make your own ground cables with some eyelets and spare battery cables. I had some extra wire laying around from stereo installs and used that.
 
Last edited:

hotcobra03

Well-Known Member
Established Member
Joined
Mar 11, 2007
Messages
7,461
Location
poteet,texas
When I've had the issue of the colts dropping as things warmed up it was the alternator. The ground might be getting finicky if its corroded inside. But mine did it with an upgraded ground as well. I went with the J2 Fab when it was on sale.

You can make your own ground cables with some eyelets and spare battery cables. I had some extra wire laying around from stereo installs and used that.

I was lazy and cheap.

Cable for lawn mower battery at Walmart.
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,128
Location
Cali
I was lazy and cheap.

Cable for lawn mower battery at Walmart.
Technically mine was laying around too. I still have some shoved into a cubby on my shelf.
I might try this for shits and giggles, would be kinda funny if the whole time everyone was scratching their head at the alternator vs obd 2 voltage reading variance was just that stupid ground wire
I should probably check what mine says at the battery compared to the datalogs. I think I saw 14.2 or 14.3 last time I had the computer hooked up. It usually shows 14.8 at first start.
 

hotcobra03

Well-Known Member
Established Member
Joined
Mar 11, 2007
Messages
7,461
Location
poteet,texas
What’s crazy.

I use my rscort radar detector.

It comes up low volts below 11.8

I seen 16 on my buddies car installing a reman. That went back fast.
 

HuntFishCobra

Well-Known Member
Established Member
Premium Member
Joined
Oct 29, 2011
Messages
1,314
Location
KS
I'm ever so slightly low on voltage from my datalogs. If this fixed it and I don't have to drop $300 on a new alternator I'd be ecstatic. My wife would be even more excited .... lol
 

HPLouis

Well-Known Member
Established Member
Joined
Sep 27, 2002
Messages
1,708
Location
New York City
Where can I find this ground upgrade? Mine has been doing the same starts at 14 on my aeroforce then at the end of my drive as low as 13.2. When I had the ac on max the other day it dipped to 12.8 a few times. I did look and mine has been replaced at one point it says remanufactured on the case. I’ll try the dvom on the battery next time.


Sent from my iPhone using Tapatalk

Mine does the same thing. I thought I was having a problem so I replaced the alternator and battery. After all that, same thing. I wasted money.

I'll check my grounds.
 

c6zhombre

E85 NutSwinger
Established Member
Joined
Sep 14, 2008
Messages
5,430
Location
League City, TX
This has been brought up a lot in the past.....why does the PID read so much lower than at the battery? No one ever came up with a definitive answer. I know mine reads .4~.5 difference. I can see the log.....the pid volts are logging 12.5 in summertime brutal heat....but yet WOT I'm still hitting 11.5 AF on the wideband.

The only time driving this car did I have a serious voltage issue my PID reading dropped to 11.8 just cruising. The car reacted very funny, almost like spark blowout on throttle input and I was like WTF? Looked down at my volt PID and saw the 11.8......limped her home, replaced the alt. All good for 3 years now. I still have all the factory grounds....but I did unbolt and clean every attachment point I could when I did the alt (a reman btw)
 

MaxxdSVT

Active Member
Established Member
Joined
Nov 27, 2016
Messages
167
If I get a big 3 upgrade kit, will it be fine to do that with stock alternator? And if so, what amp fuse would I use for that? Would 250 amp fuse be overkill?

Sent from my SM-G960U using the svtperformance.com mobile app
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,913
Location
Central Fl
If I get a big 3 upgrade kit, will it be fine to do that with stock alternator? And if so, what amp fuse would I use for that? Would 250 amp fuse be overkill?

Sent from my SM-G960U using the svtperformance.com mobile app

it would be fine but overkill for sure (and doesnt address the wire he's talking about). Just to be clear, the wire hotcobra is talking about doesnt actually increase voltage, it just appears to let you see correct/actual voltage via the obd2 port
 

olympic

Well-Known Member
Established Member
Joined
Dec 28, 2014
Messages
3,510
Location
Canada
I have 0 gauge + and - wires running direct from the battery to alternator, upgraded the wire to the fuse box and added a couple chassis grounds and it still reads 0.5v low on my Aeroforce gauge and datalogs.
 

c6zhombre

E85 NutSwinger
Established Member
Joined
Sep 14, 2008
Messages
5,430
Location
League City, TX
it would be fine but overkill for sure (and doesnt address the wire he's talking about). Just to be clear, the wire hotcobra is talking about doesnt actually increase voltage, it just appears to let you see correct/actual voltage via the obd2 port

If just swapping that wire fixes the voltage PID snafu....I'm definitely going to try it! I hate seeing that difference

You guys trying this....please report back with results
 

Users who are viewing this thread



Top