Battery boffins required

[DannyVTS]

Had another problem with the Saxo, after getting the gearbox done and replacing the manifold this afternoon the electrics started playing up and the battery went dead.

Took the battery out tonight and its a "intelligent" one, which is telling me to replace it. A friends bringing me a battery tomorrow BUT I have a few questions.

• How the hell does it know that it needs to be replaced?
• Is it accurate?
• Is there a way to stop it happening again?

This is the battery


Pretty cool eh?

[Adam_W]

looks like every other battery iv seen, the "light" on most i have owned was black despite the thing working fine, I have also noticed that if you tilt the battery the colour changes, so its probably the fluid level or something.

Have you checked it with a meter?

[DannyVTS]

Just checked it with the meter now and its showing a healthy 13v, which is annoying. Its definitely dead, I can't get a current reading from it !

[joewilliams]

DannyVTS said:

Just checked it with the meter now and its showing a healthy 13v, which is annoying. Its definitely dead, I can't get a current reading from it !

Er... how are you attempting to get a current reading?

If you've set your multimeter to a current range and connected it to the battery terminals, you'll have blown the fuse in your meter.

I = V/R
Current = Voltage / Resistance

Voltage is reasonably constant, resistance varies according the the load, current varies to match. Your meter has close to 0 ohm resistance = close to infinite current. For a very short period of time

[Eggman]

It's a hydrometer - there's a clear plastic rod hanging down into the electrolyte with a coloured ball that either floats or doesn't depending on the state of charge. For what it is it's fairly accurate, but it can only tell you about the state of one cell - it could be fine, but the next one might be screwed and the battery scrap. Best thing with batteries is to test them with a multimeter and bin them at the first sign of trouble.

[Astra Dan]

If it's showing 13V then it might not be that bad - it'll at least spin the motor. It might pretty much croak under heavy load, but it's not 'dead'. As you have a French car I'd suspect the starter solenoid or somehitng if you're getting absolutely nothing from it. Not even ignition lights?

[DannyVTS]

I can crank the car and turn it over, or I can atleast engage the starter motor and hear it working but the battery is not strong enough to crank it fast enough to start if that makes sense..

[littleredrooster]

Has it not just gone flat? Have you tried charging it?
13v static means little or nothing. It's voltage under load you need to measure.

[Baz Tench]

As mentioned above, it may have a dead cell. All will still seem fine and dandy until you put it under load...

[HellDiver]

Get a spanner. Wrap it in a diesel soaked rag. Place it across the battery terminals, while it's in the car. The car should burn to death, at which point it's finally out of it's misery, and ours.

[Night Runner]

HellDiver said:

Get a spanner. Wrap it in a diesel soaked rag. Place it across the battery terminals, while it's in the car. The car should burn to death, at which point it's finally out of it's misery, and ours.

Helpful as always

[HellDiver]

Aw come on, he's on here every other day with some sort of motoring disaster with that French stbox. Do a search, you'll see.

[jmorgan]

Battery just went sarf on one of mine. Charge voltage was OK when running so it was getting a good charge voltage. Checked current draw with all off to make sure there was not a fault dragging it down overnight and when it had had a decent charge the volt meter showed and instant drop from 13.8 volts to 7. It was seven years old though

Edit. The indicator in mine reckoned it was OK.

[Prof Prolapse]

HellDiver said:

Aw come on, he's on here every other day with some sort of motoring disaster with that French stbox. Do a search, you'll see.

LOL!

OP, as mentioned I think it would be amps that are the issue.

You'll need a specialist multimeter too avoid popping the fuse as, I think I'm correct in saying, that most boggo multimeters are only good to 10A.

Can't help more than that as I'm not a battery boffin.

ETA: More info on battery ampage testing etc.

http://www.aa1car.com/library/2003/us20310.htm

Edited by Prof Prolapse on Sunday 27th February 13:39

[Ozzie Osmond]

Your battery is knackered, pure and simple.

A battery can be knackered either by,

a) inability to deliver current. This is when everything seems to work but there's not enough juice to crank the engine properly. A specialist battery centre can test for this with a high current drain test.

b) inability to deliver voltage. This is when you get a reading below 12v and is often due to one or more defective cells in the battery.

Modern car electronics are highly sensitive to voltage and it's not unusual to start getting electrical gremlins on a car which will still start OK. Voltage drop during cranking phase triggers all sorts of warning lights and failures.

You need a new battery....

[rossw46]

joewilliams said:

Er... how are you attempting to get a current reading?

If you've set your multimeter to a current range and connected it to the battery terminals, you'll have blown the fuse in your meter.

I = V/R
Current = Voltage / Resistance

Voltage is reasonably constant, resistance varies according the the load, current varies to match. Your meter has close to 0 ohm resistance = close to infinite current. For a very short period of time

Yup...big mistake.

Your meter would need to be in series with the load (ie heaters,lights etc) BUT be careful you dont exceed your meters fuse limit.

I wouldnt think you'd want to know anything to do with the current when determinig if your battery is knackered,all based on the voltage of the battery.

[Ozzie Osmond]

rossw46 said:

Your meter would need to be in series with the load (ie heaters,lights etc) BUT be careful you dont exceed your meters fuse limit.

Most meters can only read tiny currents. A car battery can deliver 80 amps or more. For goodness sake at least make sure you have some knowledge of the subject before dispensing advice. Without sufficient battery ability to deliver "current" the car won't start. Voltage drop occurs when current is drawn from the battery.

If you think of a battery like a water tank and plumbing system,

Voltage = pressure (the height of tank above the tap. Tap might run quickly but tank will soon be emptied if it's too small)

Current = flow (principally the amount of water in the tank)

[rossw46]

Ozzie Osmond said:

Most meters can only read tiny currents. A car battery can deliver 80 amps or more. For goodness sake at least make sure you have some knowledge of the subject before dispensing advice. Without sufficient battery ability to deliver "current" the car won't start. Voltage drop occurs when current is drawn from the battery.

If you think of a battery like a water tank and plumbing system,

Voltage = pressure (the height of tank above the tap. Tap might run quickly but tank will soon be emptied if it's too small)

Current = flow (principally the amount of water in the tank)

You obviously missed the bit where I advised to be careful of measuring current that will exceed what the meter can read.

I am aware of how batteries work,spent a little time at uni,but thanx for the lesson anyway

[Ozzie Osmond]

rossw46 said:

I am aware of how batteries work,spent a little time at uni,but thanx for the lesson anyway

Your previous contribution was plain WRONG but I was polite about it. Hope you've put your degree to better use elsewhere. Show me a multimeter likely to be available to OP with a fuse which can stand car battery drain current and I will be impressed. Until then, best to keep quiet.

[rossw46]

Ozzie Osmond said:

Your previous contribution was plain WRONG but I was polite about it. Hope you've put your degree to better use elsewhere. Show me a multimeter likely to be available to OP with a fuse which can stand car battery drain current and I will be impressed. Until then, best to keep quiet.

http://cgi.ebay.co.uk/High-Quality-MS2108-True-RMS... (not through a fuse,but would read.Propbaly isnt very good quality)

Thank you for being so polite.Most meters have a 10 Amp range,which if put in circuit correctly could measure currents where,for example the radio was turned on,or some other load was turned on that would not draw a current of more than 10 Amps.I did not suggest that he put an ammeter in series and crank the engine!


I also said he need not look at the current drawn from the battery,as I realise he will likely not have the equipment needed to do it.

Oh,and current does not equate to the amount of water held in your hypothetical tank,rather the rate at which this water would flow out of or into the tank.

I will keep quiet now.

Edited by rossw46 on Sunday 27th February 15:35

Edited by rossw46 on Sunday 27th February 15:38