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Discussion Starter #1
OK, stupidly left my car for a few weeks and the battery is totally dead. Put it on charge, and initially it took no current. Left it on for a half hour or so and it started taking 2a. After a few hours it's now taking 6a. Anyone know if this is normal? The battery is fairly new, it's got a 3 year warranty, so if there's any easy way of diagnosing a stuffed battery I'd like to know, so I can have a go at getting a replacement!
 

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I know that some of the maintainance free batteries can take between 12 - 18 hours to fully charge, ie bosch silver, I am not sure if the current that the battery is taking changes over that period.
 

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Maintenance free batteries do take a long time to charge.

You should be monitoring the terminal voltage while charging.
Log the voltage every hour using a digital volt meter.
It will keep rising.
When it hasn't risen for an hour, the battery is probably fully charged. At which point the voltage while charging will probably be around 15V

BUT, what is the capacity of your charger?
If it is less than 10A you are probably just waisting your time.
 

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Discussion Starter #4
Charger capacity is 12a. I had it on for a few hours last night. Just connected it up, and it's taking 7a at 12.6v. I tried it on "boost" charge for a few minutes, took 10a at 13.4v but the current needle kept flicking to 0a every now and then which didn't seem healthy so I've turned it to normal charge. Thanks for the info about the voltage rise, I'll keep an eye on it over the next few hours :)
 

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As has already been said, 12-18 hours is normal for charging modern batteries.
If you are trying to do it by only charging for a couple of hours at a time it will take a LONG time!
 

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Discussion Starter #6
As has already been said, 12-18 hours is normal for charging modern batteries.
If you are trying to do it by only charging for a couple of hours at a time it will take a LONG time!
Ta, I only have about 3 hour a night between getting home and going to bed at the moment! I know it will take a few evenings, I've got a different battery in the car for a while, I'm not actually using the car at the moment as I need to do some MoT work; I'm just trying to keep enough juice for the alarm and radio!
 

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Be warned that high speed Boost charging knackers battery life, much better to charge it more slowly.

Cheers,
TB
 

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Discussion Starter #8
What sort of current would you say "boost" starts at? I was worrying about the same thing, with the charger I have the lowest setting pushes out 7a, so I figured it would only take 10 hours or so to charge?
 

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Charging at 8A would be no problem and would take all day.

I have an old Halfords 10A charger and that just has "High" or "Low" settings. "Low" is just a trickle charge. To charge from flat needs the "High" setting, which as I said still takes all day.
 

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'Rule of thumb' charge at 1/10th the amp-hour rating of the battery. That way you should avoid buckling the plates. Even better use something like an Accumate which monitors and checks charging automatically and can be left 'hooked up'.
 

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Discussion Starter #11
'Rule of thumb' charge at 1/10th the amp-hour rating of the battery. That way you should avoid buckling the plates. Even better use something like an Accumate which monitors and checks charging automatically and can be left 'hooked up'.
Nice one, 70Ah battery, so the 7a ish I've been seeing should be OK :)
 
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