flat battery -HELP

[carnut13]

My partner has a mini and shes left the lights on overnight and all day!

How long should it take a battery charger to recharge to the point of getting the engine to fireup? I dont want to try prematurely and go backwards on the charge capacity and its over 30 years since Ive had to do this so my memory is not up to this question

I need to sort this now as she has to go to work tomorrow early and Halfords ( if I need a new battery) are only open til 8pm

 

[colechelle]

depends on how good the charger is and how good the battery is, it would have to be a super charger to put a desent amount in to start before your deadline!!!

 

[Xtractorfan]

A good battery should restart a car with around a one hour charge, as the battery is flat I would take advantage of this and trickle charge it overnight..it will rejuvenate the battery make sure the cells are properly topped up

 

[carnut13]

Thanks guys

 

[television]

As Cole above,,, sometimes a battery will come up quickly.

My V70 did not get used for 3 weeks and the starter would not turn it over, but after 1 hour it did. this was charging at 4 amps. the battery is nowhere near charged at this point and I did what I had too in the car and put it back on charge for 9 hours

Halfords batteries are awful

 

[television]

I did note that one recommendation posted elsewhere was very wrong,, you should never use the alternator for charging a flat battery ,, bad for car and alternator.

If the battery is flat,,this will allow the voltage to rise above the 13.8 volts and could blow many things until a little charge was put into the battery,, once the voltage has settled then the max charge rate is at 1.3 volts and would take a drive from here to Scotland

 

[carnut13]

Thanks for the prompt advice to all above. This forum is certainly useful and very on the ball

Car battery charged in under 2 hrs and all is now apparently OK ( til tomorrow at the crack of dawn ?)

 

[andy_burnton]

Battery Charging

As a general comment I was always told that you should avoid charging a battery quickly.

The quicker you charge it the more heat is produced as a byproduct. This heat can warp the plates of the cells in the battery. If two plates in a cell touch, then that cell is a dead shortand you lose 2 volts from your battery's overall potential (12v batteries are generally made up of 6 x 2 volt cells attached one after the other).

You should always charge a lead acid battery on a trickle charge overnight if possible.

You may have been lucky with the quick charge, but I wouldn't make a habit of it.

Cheers,

Andy

 

[wireman]

If you realy want the proper story about charging lead acid batteries try looking at the web sites of battery manufacturers.

The rule is simple for boost charging never more than 15 volts, let the battery take whatever current it can, This rules out those booster things which will put about 20v on your battery and ruin it.
Never leave 15v on permanently ie more than an hour or three, and dont allow it to get hotter than just warm to touch (40C).

The alternator is voltage regulated and will produce around 14 - 14.4v at its terminals, there may be a slight drop in the 14.4v as a result of electrical loads on the vehicle but if it gets less than 13.5 volts the will be next to no energy being stored in the battery.
If you are not getting >14v at the battery it will take for ever to fully charge the battery, and unless you are running 24/7 you will always have a part charged battery and this is bad for its health and life.

At around 14v a flat battery will draw a heavy current for a while and then the current will fall of as the battery gets about 50% charged, it will then take at least 10 hours to get up to 90+% capacity.

A fully charged battery can be left permanently connected at 13.8v known as the float charge voltage under which conditions it will draw a very small current <1/10A, hence motor vehicle alternators should always produce more than this voltage.

Dont pass a current greater than 1/10th of the A/H rating, i.e. for 100A/H use 10A max for about 15 or more hours.

A lead acid cell has terminal voltages of 1.8v flat, 2.25v healthy off charge, 2.35v float charge and 2.5v max. The true voltages are temperature dependent and as the temp goes up the cell voltage falls at about 20mV/degC.

Technicaly the cars alternator is the best charger you can have (its temperature copmpensated), but it takes at least 24 hours to fully charge a battery @14.4v and that's an awfully long journey.

As has been said taking your time is the only good way to charge a battery.

 

[television]

The above by wireman is dead right and thank you