Battery Voltages

[Golf-Fiend]

Afternoon all

Battery/starting oddness.

Had a new battery back in August 2019. A Bosch S4 008 type 096.

Recently it's been a little sluggish on the Starts. Thought it might be a dying battery or alternator. Did some tests as follows. Car has been stood for over a week now.

Volts static 12.16

Ignition on 11.65

Cranking 9.80

Idle 14.23

Revs at 2000 14.50

 

Don't use the car for many short trips. Last two were 160 and 220 mile round trips.

 

Bit worried about the cranking volts. Is this normal? Temp was cold and dank 6⁰C. I previously had cleaned all earthing points during furlough in 2020.

 

Car is 2004 2.0 TDi BKD engine.

 

Any thoughts?

[Warrior193]

Hello, static voltage is not too bad, 9.8 on cranking is a bit low and probably explains sluggish starts. Alternator output looks ok. Are you able to get a recovery voltage reading of the battery (without engine running) immediately after cranking?

Do you have access to, or know someone with a good battery tester? 

[Camlobe]

Broadly, I agree with Warrior.

 

The cranking voltage is definitely on the low side, and that probably explains why cranking is sluggish, but that just changes the question to why is the cranking voltage low and what can you do about it.

 

My assumption is that the battery itself -decent brand, relatively recent - is unlikely to be the cause, although you can go around the circuit looking for where the voltage drops are. 

 

It is probably also worth noting that, since this is a fairly rapidly changing voltage, you can get a different absolute value depending on how closely you, or your test equipment, looks.

 

I'd be tempted to re-look at the cleaning of the high current connections. Remember, with the high currents involved, it only needs a slightly suspect connection to cause a problem. Potential clue: if any part of the circuit gets warm after cranking, concentrate your attention there.

 

Alternatively, you may have detectable voltage drops, although looking for those may be a two-person job, due to the need to have the dexterity of an octopus, all while the engine is cranking.

[Golf-Fiend]

Thanks for the replies. Sorry, not had chance to investigate further as I've been suffering from a particularly bad back. When it's better I'll do some more investigation and update my findings.

 

It seems to be just the first crank of the day is sluggish. Subsequent starts, even with 4-6 hours between are fine.

[Warrior193]

That could possibly suggest a slightly weak battery. Strongly suggest a decent charge cycle, then a good battery load test. 

[pikpilot]

I had my battery replaced in April and it came with a warranty that states "the car must be driven for a minimum of 2000 miles per year or pro rata to avoid sulphation of the battery."

I mention this in case it has had low usage in the past. 

 

[Golf-Fiend]

Well, it seems to be starting OK in this weather (fingers crossed).  I guess I'm driving it more rather than cycling to work at the moment. I'll get it properly tested in Jan when it's in for a brake fluid change.