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997.1 Charging - what voltage at the battery?

d2000

Member
Joined
8 Nov 2014
Messages
10
Hi all,
What voltage should i get across the battery with the engine running?!

Car has been sluggish when starting for a while, but let me down this evening and needed a jump start. I'm trying to determine if it's just time for a new battery, or something more sinister - have only had the car a couple of months so don't know how old the existing one is, but as its a Bosch S4 on an 05 C2S so i'd guess it's not that old.

I'm getting 13v at the battery when the engine's running - and it stays pretty constant when revved - so think the Voltage Regulator is still good ...but from other cars I've worked on, i'd have expected more like 14v - so wondering what the norm is?!

Many thanks
 
With a battery that is in any way discharged (e.g. just after starting) you should be getting @14v.
As the battery becomes more charged the voltage will drop to around 13v so I would suspect that the voltage regulator on your alternator is not working if you are seeing a constant 13v
 
Mine's an 06 and it's had two replacement batteries and I suspect it needs another one. At start up the alternator makes 14v at the battery. Altenator was new this summer.

Nick
 
Thanks both -
have ordered a new (bigger) battery ....mainly because it's the easiest thing to change! - but realistically it sounds like the alternator needs some attention.

I want to try and get the voltmeter onto the back of the alternator and check that i'm not getting a voltage drop in the wiring to the battery ...but could do with smaller hands - there's not much space in there! - will give it another go tomorrow. Fingers crossed it's only 13ishV there too and it's only a new VR that i need

Cheers Dave
 
d2000 said:
Hi all,
What voltage should i get across the battery with the engine running?!

Car has been sluggish when starting for a while, but let me down this evening and needed a jump start. I'm trying to determine if it's just time for a new battery, or something more sinister - have only had the car a couple of months so don't know how old the existing one is, but as its a Bosch S4 on an 05 C2S so i'd guess it's not that old.

I'm getting 13v at the battery when the engine's running - and it stays pretty constant when revved - so think the Voltage Regulator is still good ...but from other cars I've worked on, i'd have expected more like 14v - so wondering what the norm is?!

Many thanks

Dave, you'll see more than one thread about batteries going off in 996/997 and possibly probably older. It's not unusual for this phenomenon to appear in cars which don't do a lot of mileage, cars which have alarm systems, trackers drawing down current. For example in winter driving conditions (lights and wipers) I can run my battery down gradually on a 3 miles each way three days a week pattern especially if I don't give him a decent run weekly. I now remember that I could do the same with the MGF.
So, even with a new alternator and battery and a 14 volt charge on the dial, the engine's not running for long enough to replace the charge which is used.
 
d2000 said:
Hi all,
What voltage should i get across the battery with the engine running?!

Car has been sluggish when starting for a while, but let me down this evening and needed a jump start. I'm trying to determine if it's just time for a new battery, or something more sinister - have only had the car a couple of months so don't know how old the existing one is, but as its a Bosch S4 on an 05 C2S so i'd guess it's not that old.

I'm getting 13v at the battery when the engine's running - and it stays pretty constant when revved - so think the Voltage Regulator is still good ...but from other cars I've worked on, i'd have expected more like 14v - so wondering what the norm is?!

Many thanks

Dave, you'll see more than one thread about batteries going off in 996/997 and possibly probably older. It's not unusual for this phenomenon to appear in cars which don't do a lot of mileage, cars which have alarm systems, trackers drawing down current. For example in winter driving conditions (lights and wipers) I can run my battery down gradually on a 3 miles each way three days a week pattern especially if I don't give him a decent run weekly. I now remember that I could do the same with the MGF.
So, even with a new alternator and battery and a 14 volt charge on the dial, the engine's not running for long enough to replace the charge which is used.
 
My previous gen 1 measured around 14v when charging too, and from memory went down to about 9.5v (?) when cranking over.

Also worth mentioning the main battery/alternator/starter motor lead. I changed mine due to poor HOT starting (high resistance in the cables), which is often confused with battery not charging. Doesn;t sound like it in your case though, but thought it was worth mentioning.
 

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