Car battery charging ... need some advice

2pack · 26-02-2013 10:42AM #1

hi,

I charged up to batteries and went to start my car and neither would start them, i had put multi meter on them to check voltage and one was 12.98v and the other is 12.96v which i assumed was good as the other one that originally come out of car is about 12.96v or so too charged now and started my car first turn so i really do not understand these voltage readings.,. can anyone explain please as these two were fully charged and showed good voltage but were as good as dead

Ta

JoeySully · 26-02-2013 10:58AM

are you checking them immediately after charging. If so give them an hour and check again. If the voltage has not moved then the battery should be good.
Id check your terminals / jump leads to ensure they are clean.

2pack · 26-02-2013 11:14AM

ok i checked them again and one is 12.58 and other is 12.81 but should these still not have started the car... what voltage do they need to be? Ta

bbam · 26-02-2013 11:21AM

We're you installing these batteries correctly or via jumpleads?
The best result will always be through connecting them correctly, jumpleads often need to be fiddled round to get a good connection
Think about jumpleads, the points of contact can have a small surface area, this can struggle to get enough energy through to start a car if it's own battery is flat or out. The proper battery pole clamps wrap right round the pole so the contact area is much bigger, allowing huge amounts of current to flow easily.

bigtimecharlie · 26-02-2013 11:23AM

At least 14v should be on a charged battery before attempting to start a car.

shooter88 · 26-02-2013 02:03PM

bigtimecharlie wrote: »

At least 14v should be on a charged battery before attempting to start a car.

Is that not what it gets charged by?

tossy · 26-02-2013 02:11PM

What kind of car and engine is it ? Should be enough to turn over a small car but a bigger diesle engine might not be.

When it comes to the starting of a car the important figure on batteries is 'cranking amps' not voltage per say - although if the battery has no charge then it wont start anything.

T-Maxx · 26-02-2013 02:13PM

Voltage alone won't cut it - you need amps as well.

kona · 26-02-2013 02:15PM

Have to checked the water level in the battery? Just because its charged and reading 13v it could still be fit for the bin.

2pack · 27-02-2013 08:08PM

bigtimecharlie wrote: »

At least 14v should be on a charged battery before attempting to start a car.

i never could get a battery to 14v when charging it,

im trying to start a 2003 passat tdi, i was going by how much voltage battery had when fully charged...

ironclaw · 27-02-2013 08:16PM

2pack wrote: »

i never could get a battery to 14v when charging it,

im trying to start a 2003 passat tdi, i was going by how much voltage battery had when fully charged...

Are you getting any power to the car? i.e. Lights on the dash?

By the way, its entirely possible to have 12V on the battery and be unable to start a car. You need current (And alot of it) The average car could pull a couple of 100 Amps for a fraction of a second during starting. Thats why you can't start a car with some AA's.

Power = Voltage * Current

So 6V at 2 Amps will supply the same power as 12V at 1 amp. If you have a dud battery you won't have any current capabilities. The voltage is irrelevant as you could start a car as low as 11V before the internal ECU will knock it off due to a low battery warning. Likewise it could be 14V and it will still internally regulate to 12V.

As has been said, directly connect the batteries. Check polarity and clean the contacts with some alcohol (Not with the battery present!) If it doesn't start, you probably have a dud cell / battery.

Avns1s · 27-02-2013 09:16PM

Try jump starting from another car. I'd have my doubts that the batteries are your problem.

whizbang · 27-02-2013 10:57PM

When batteries die, they loose their capacity to store power. The will still charge up to voltage, but cannot deliver this voltage at big currents.
A sure sign of a bad battery is that it charges up quickly. A new(discharged) battery could take 48 HOURS to charge with a 3amp home charger.

Fit the battery in the car, turn on the ignition and headlights, and measure the voltage immediately. should be 12.4-12.8volts.
measure again after 5 mins. If voltage is below 11volts, bring it straight to recycling.(and get paid!)
more than 12v, keep it in the car, its good.
Between 11v,12v keep it for backup.

Measure these voltages directly on the battery lead posts. and Measure also engine block to starter or alternator at the same time.
If there's more than half a volt difference, then you have a wiring problem.

2pack · 27-02-2013 11:28PM

Charged one of them today again and showing 12.97v now but battery was hot and started to smell, turned it off as soon as i could as could have exploded

Is them pulse chargers any use or a waste of money

whizbang · 27-02-2013 11:45PM

To test your battery, a 60watt headlamp bulb on a good battery will last over 10hours. -but dont leave it for that long.

a good battery will read over 12.6volts with bulb connected. If voltage is less than 12volts after 1 hour, the battery is dead.

chargers can go to over 15volts when charging.

shinkansen · 28-02-2013 12:03AM

2pack wrote: »

Charged one of them today again and showing 12.97v now but battery was hot and started to smell, turned it off as soon as i could as could have exploded

Is them pulse chargers any use or a waste of money

buy a battery from a motor factors and use that?

messing around with battery's is a bad idea

FWIW many battery's lying around long time are probably dead, especially SLA ones.

Car battery charging ... need some advice

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