In the hidden menu i have a 13.9v reading for the battery, is that a good reading or is its life cycle close to its end? How reliable is that reading?

 

mine got 14.2 when car is on and 12.3 when off. I tried once left the car for a month and its 11.9v and it still starts, just.

 

You should see ~14v when the car is on as the alternator is outputting additional voltage to charge the battery. If your voltage is much higher than this your voltage regulator is bad and you start running the risk of ruining your battery and electronics. Lower and either the voltage regulator or the alternator itself are bad and your battery isn't going to properly charge.

When the car is off you're seeing the voltage of the battery itself, which should be a little over 12v. Lower and your battery isn't fully / properly charged.

Edit: To directly answer the question for the OP, that number doesn't tell you anything about the battery - you need to check with the car off to test the battery itself.

 

I agree with most everything you said, but while testing with the engine on, do put a moderate load on the engine (give around 2000 rpms). This will give a better test to your alternator. A weak alternator will present itself when not able to handle a moderate load above (2000rpms). If voltage is above 14v then like he said, voltage regulator might be bad.


To answer the OP, I wouldn't worry about the readout of your battery voltage. As it sits, the voltage will drop slowly but as long as the battery can hold a charge, your CC Amps is the real factor in a weak battery. If your battery is failing, you will notice a weaker, slower start. Until you notice a weak start, I wouldn't worry about your battery.

 

I have noticed a strange start... it ignites ok, but then kinda not getting the revs up, plus the fact that i can hear a rattling sound, as if the engine isn't working well but that goes away after 3-4 secs! In the past 4 months ive had had this twice when i started the car and it was both on a pretty hot day!

 

Sounds like the symptoms of a dying battery. I would start doing research and pricing out a few. I don't know where you normally buy batteries, but if there is an autozone near you, they can check the CCAmps which should give you a pass/fail type indication.

After have a few incidents in my last car (mustang) with a dead battery, I now replace my battery after the second slow or weak start. I'll easily sacrifice a couple months of iffy battery life for a new reliable battery.

 

But only twice in 4months and only on a hot day? Are those symptoms of a dying battery?

 

normal

 

Well, you will likely see it happen again soon, generally 1 weak start is not a problem, just know that every time it starts weak, the battery is more and more finished.

When you get 2 weak starts a week apart, you will have even less time to find a battery and replace it.

So you can wait for 2 weak starts in a month or a week it's up to you, but that would definitely be a sign of a dying battery. Lead Acid batteries are really bad with extreme temperatures (hot/cold), and with temperature variation (one day hot, one day cold).