Car Battery Charging.

[Doug Ireland]

Hi Folks, it's been quite a while since I've been on the forum.

I have a flat car battery that I'm charging with an iCharger 1010B+ and I have a question.

Going by what's printed on the top of the battery it has a 75A capacity and a cranking capacity of over 600A.

At present it has been charging at a rate of 2A for the past 5 hours and some 15A have been put in. My question is, how long do I let it charge for?

Cheers,

Doug.

[Phil 9]

the I charger is a smart charger so can you not just leave it until the charger says full or are you in a hurry to get the car going again

[FlyinBrian]

Assuming it is pretty near flat and If it is 75AmpHour (rather than 75A) then, at a 2A charge rate, you will need to charge for 75/2 = 37.5 hours = plus about 10% to allow for losses, so say 80 hoursish.

If it is charging at 2A It can not have put in 15 Amp Hours in 5 hours, it would be 10 AH.

[Jonathan M]

Why did it go flat in the first place? Maybe its damaged beyond the ability to accept a full charge? (Lead acids don't like being discharged much below 50% capacity.) What is its voltage?

Re your original question, one can carry on charging a lead acid battery indefinitely:  once its full (i.e. up to full voltage) it won't accept any more amps, so to speak.

Edited By Jonathan M on 20/09/2016 20:04:26

[Doug Ireland]

Guys, the battery is less than two years old and was in my 2004 X-Type Estate. I went to start the car after leaving it for a couple of months and it was completely flat. A check after I removed it showed just over 1.8vdc. Obviously my charger would not start at this voltage so it took three days with a Solar Powered charger to bring the battery voltage up to just over 12.

This picture was taken about half an hour ago. Seems like it's working.

[Denis Watkins]

Lead acids too have to endure vibration and potholes while travelling in the car, and can drop a cell due to internal plate damage at any time. Dropping one cell in these offers massive internal resistance and degradation.

On the bright side, this has happened in good weather and not on the 1st icy morning when you cannot easily overcome the delay

[Denis Watkins]

Having read more of your post, lead acid will not tolerate this low, flat state for very long, and even if the battery recovers for a short time, it is damaged.

In days of old, batteries were built stronger, but 2 years is a long time with modern batteries. 12 months is the usual guarantee, unless you buy top dollar 75A

[Steve Hargreaves - Moderator]

Have to agree with Denis here....if the voltage has dropped that low it sounds like something inside has degraded...I very much doubt it will recover to anything like full strength & will probably let you down at the first cold spell....

Try Eurocarparts for a new one....they often have 30% off weekends too so keep an eye out.....that said it's probably peak battery buying season so discounts might be hard to come by....

[Peter Miller]

As point of interest you can buy solar cells that you plug into the lighter socket and leave on the top of teh dashboard. They will keep it topped up for ages. My spare 12 volt battery has been sitting on one of thes for nearly two years and still read 12.75 volts. They are not that expensive.

Mine came from Amazon.

I first used mine in mid winter to keep a car battery charged outside while waiting to sell the car, It was there through frosts etc for about 6 weeks. Started first turn of the key

[Doug Ireland]

Hi Peter, I have one that I used to use in my car before I bought the new battery as the old one would run down after a couple of weeks sitting on the driveway. If I can rescue this battery then I start using the solar charger again.

[Peter Beeney]

Doug,

With the greatest respect, but if you leave the motor standing for any length of time you really need to periodically charge the battery or disconnect it; these days I think there is always some small permanent discharge going on, even if it is only a flashing led. Over time the battery will eventually go completely flat.

The positive plate in a lead acid cell consists of lead dioxide and the negative plate is made of lead. During discharge the negative plate turns to lead sulphate. If this is not changed back by recharging fairly quickly it start to harden which will only get worse over time. The harder it gets, the more difficult it is to recharge. They can be recovered though, I’ve seen some pretty desperate cases successfully brought back from the brink in the past.

Leave your car battery on charge until it reads at least 14 volts. The car’s alternator charge level will be around 14.2 - 14.4 volts. You can leave a lead acid permanently floating across a charge voltage of 2.3 volts/cell, that’s 13.8 volts for the car battery. This keeps it in tip top condition without overcharging it.

I rarely give up on anything until it becomes obvious that it’s not worth pursuing further…

Good Luck!

PB

Edit - If you remove the battery for storage make sure it’s really fully charged first. Then it will stand quite a while. If it’s discharged, perhaps by only a small amount, it’s most likely to carry on self discharging, which then rather defeats the object of the exercise.   

Edited By Peter Beeney on 20/09/2016 22:01:27

[Former Member]

[This posting has been removed]

[Peter Christy]

That's the problem with modern cars - there is always something drawing current, and it will flatten the battery fairly quickly if left unused.

The old battery might be useful for starting models, but its days as a reliable starter for a car are over.

I've found that the cheapest batteries you can buy from Halfords are way better than the "name" brands for longevity! (Yes, really!)

Both my cars (one 21 years old, the other 45 years old) have cheapo Halfords batteries in them, and one has been going strong for over 5 years now - the other has only been in there three, but still starts instantly.

--

Pete

[Shaunie]

Do not add acid unless it has been spilled. When a battery dries out only water leaves the cell, replenish with DI water only.

Lead acids are a topic all on their own. Visit battery university for loads of useful info. Basically, do not run them too flat or for too long, when recovering them keep the current low until fully charged or at least until they have trickled for some time and check the voltage, 14V for regular types, 14.5 for Calcium. The longer they are flat the more permanent the damage.

Shaunie.

Edited By Shaunie on 20/09/2016 23:31:35

[Nigel R]

"I've found that the cheapest batteries you can buy from Halfords are way better than the "name" brands for longevity! (Yes, really!)"

If I remember right, Halfords own brand are rebadged Varta (Silver?). But not their "A" grade product. The Halfords ones are (somewhat predictably) a little looser in the quality department - you might get a good one - or you might not. From memory Halfords are rated a bit lower in both total capacity and CCA.

Having said that both our current cars (and some previous) have Halfords batteries, and they're holding up just fine.