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How do I differentiate between a battery that has simply discharged and one that needs replacing ?

I have a multi-meter.

The car is only used infrequently and often seems to happen with Breras, the battery drains when stood for long periods.
 

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Drive it to Halfords and ask them to test it:for free they will give the anti on the Battery and alternator.
 

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Well, got into my car this afternoon and the pressing of the start button caused the entire display to switch off. I removed the battery and put it on charge and it was taking a lot of amps.... The car hadn't been used since last Wednesday and the battery is at least 2 years old so I thought it was time to bite the bullet and get a new one on order. Fortunately I won't need the car until the middle of the week.

https://www.tayna.co.uk/EA900-Exide-Premium-Car-Battery-115TE-P9593.html

is on the way for Tuesday I hope!

Guy
 

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Using a multimeter, you should get 12.8v, anywhere between 12.5v-12.9v should be fine, between 13.2v and 14.5v when the engine is running. If your not using the car much, get a maintenance charger, I use the CTEK MXS 5.0, works very well and has the added benefit of pulling batteries back from the dead with its recondition mode. With its quick connect plug, its very easy to use with minimal fuss. I did have a dead cell on the Spiders previous battery and the voltage dropped to 10.5v, once this has happened, the battery is dead. If you can get the battery fully charged, but it drops voltage, chances are the battery needs a pulse charge from a charger with a recondition mode. Ive done this with a few batteries now and after its been reconditioned the battery act like brand new.
 

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I had a Fiat Punto before the 159 and it's battery died in 8 hours, it was fine in the morning on the way to work but left me stranded when I needed to get home. Ended up paying for a taxi in each direction which cost more than the replacement battery! The current battery is on charge and has been drawing current for 6 hours now but the rate of charge is dropping so it's not completely dead yet. I use a CTEK to keep the Stratos rep battery in a good state, it can be weeks between use but as the Alfa lives on the drive in the open the use of a CTEK poses problems.... But still a good suggestion thanks!
 

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Hey there, had a couple of odd electrical issues on the 159.
The HIDs refused to works last night (sidelights fine). Turned engine off and on again and fine since then.
This morning gave a warning about high radiator fluid warning (this later issue is from the GF and said boot wouldn't open with the key).
Had a look at the battery, the negative terminal connection seemed a little loose (rotated freely but not 'loose' if that makes sense).
Cold voltage measured at 12.2V. Battery is around 3 years old.
Firmed up the terminal connection, but is that voltage on the 'dead' side? It was driven this morning.
 

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Had a look at the battery, the negative terminal connection seemed a little loose (rotated freely but not 'loose' if that makes sense).
Cold voltage measured at 12.2V. Battery is around 3 years old.
Firmed up the terminal connection, but is that voltage on the 'dead' side? It was driven this morning.
12.2V is officially flat, needs charging.
Can go that way if the car is only used for short trips or is left standing.

If it is still starting the car I'd say it just needs a proper charge, a proper long drive may bring it up, or it may need hooking up to a charger.


3-years could be heading towards the end, depending on the quality of the battery and how the car is used.

The loose terminal won't have been helping though.
 
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Voltage tells you next to nothing about the health of a battery...you could charge a knackered battery for an hour and get a good voltage reading...but it would only be a surface charge with no ability to deliver serious amps...and it's amps that start engines...not volts. A very quick visual way to tell if your battery is approaching the end of its life is to look at the ends of the casing...as batteries age the plates sulphate and push apart..this causes slight outward curvature of the ends of the battery. Other than that it's a "drop test" that's required...we do this at my work to test batteries. You need to charge it as full as you can then connect the drop tester (Halfords etc will have one and test for you). Take a note of the voltage and then turn on the tester...this puts a full 50amp load on the battery. Any weakness will quickly show up as a fast falling voltage under that sort of load. This test cannot be done with a flat battery...so charge it before you test it.
 

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Be wary of halfords though, they did their test thing on my old merc ml battery and they said it was fine. It wasn't. Wouldn't hold a big enough charge for a day to start the car so I bought a new battery anyway and all was well even though Halfords machine said the knackered one was fine.
 

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Thanks all,
I've tried to tighten the connection on the battery (also realised the ignition was on when I measure it, which would have dropped the Voltage slightly). The engine still seems to start fine so I will ensure I keep an eye on it, see if tightening the terminal helped at all, and measure again relatively regularly.
 

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My 2 litre JTDm has struggled to start for the past few months when cold. When cold the voltage was almost exactly 12. The display would often throw up ABS and other faults when struggling to start. I ordered a new battery Tuesday, it arrived Wednesday and coincided with a total refusal to start and a blank display - I'd say that was good timing!
 

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Just an update, but since I resecured the negative battery terminal connection I've not had any more issues! :thumbup:
 

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Battery voltage and temperature compensation. Note voltage readings should be as long as possible after any charge / discharge and after charging I recommend disconnecting all lead from charger or car. No point measuring battery voltage if a defect on the car has flattened it!

NOTE: most batteries in your cars will be maintenance free or AGM so use those values.
 

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My method is to charge the battery then give it some discharge. Probably headlights for 2 minutes. This just 'conditions' the freshly charged battery. Then after at least an hour test the voltage. Measure, at 20c, 12.65v is 100% charged and 12.25v is 50%.
 

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Old Engineer note that voltage of AGM are less affected by temperature and the voltages for same SOC are higher. This caught me out when measuring the voltage of an AGM on my motorbike.
 
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