What is a battery?


4x4 Earth Contributer
Thought I killed my Patrol battery a couple of days ago. Its been sitting there unregistered and forgotten since the SA Bushy's meet down the sout east many weeks ago. And I had forgotten to either start the motor or put the battery on the charger every month or so.

So when I tried starting it - nothing. Pulled out the old charger - it's stuffed too. Tried to fix it. Can't find my soldering iron or solder. Went to Dick Smith - they're stuffed as well. But I picked up a few bargains at their closing down sale!

Finally found a new soldering iron. Had a go at cutting out the shorted wiring ( insulation worn through ). Gave up and bought a new one. Just a cheapie. Put it on the battery for two or three hours - nothing. Left it on the charger overnight. First thing the next morning rushed out to try again - still nothing.

Started cursing myself for being so slack. I've murdered a perfectly good battery! Left the charger connected when I went to work. Got home about 1.00pm and thought I may as well turn the key. Not expecting anything but an insipid grunt. The old girl fired up instantly - good strong spin from tyhe starter motor. Like bringing an old frined back from the brink. Sure great to hear the motor purring again.

So I had a think about what was going on. I reckon three things -

Firstly - the car had been sitting a very long time. So the battery would have been really down on charge. Much more than if it was just flat. It was REALLY flat. i.e. it was going to need a lot of Coulombs of charge to 'fill 'er up'!

Secondly, it was a 4x4 battery - much larger than a normal car battery. So, like a large rainwater tank that needs more water than a small water tank, it needed a whole lot more Coulombs of charge than would a normal sized ( capacity ) battery.

And thirdly, the new battery charger did not seem as powerful as the old one. The old one had an ammeter on the fron which measured about three Amps at the start of charging, and then it gradually dropped back to a about 1 Amp at the end.
But the new charger, when I hooked in the ammeter that I had saved from the old one, only showed 1 Amp when I first started charging.

1 Amp means 1 Coulomb of charge per second flowing through the circuit. Or in this case, flowing into the battery. I suppose the question could be asked, 'how much of that 1 Coulomb per second actually remains in the battery as stored charge ready to be released when the battery is used?'

I will come back to that question in a moment.

The point #3 I was actually trying to make was that at a miserable small 1 Coulomb per second, it was gong to take a lot of time to 'pump' a lot of Coulombs back into the VERY FLAT, VERY LARGE battery.

I estimate that the charger was connected for about 20 hours. So first converting 20 hours to seconds;

20 hours = 20 x 60 x 60 seconds = 72,000 seconds

Making an approximation that the current remained at a steady 1 Amp ( 1 Coulomb per second ) then the total charge put back into the battery would have been 72,000 Coulombs.

But the normal units for charge when it comes to batteries is Amp hours, where

1 Amp hour is the amount of charge delivered by a current of 1 Amp in 1 hour.

And siince the current was in fact 1 Amp, and was flowing for 20 hours, then

the total charge collected by the battery was 20 Amp hours of charge.

This little exercise lets me relax somewhat when I think how close my battery gets to being flattened when I use my CPAP ( Constant Positive Airways Pressure ) anti sleep apnoea machine all night.

I read that it uses about 1 Amp of current. So if it runs for 8 hours, then it has used 8 Amp hours of charge. Assuming I have been driving all day, the battery would have been fully charged. So that means it should still have 12 Amp hours of charge left in the morning to start the motor.

And that seems to make sense, since I have never had a problem on the many times I have actually done this exercise on my road trips. But if I were to camp for two nights in the same place, with no driving to recharge, I would be getting pretty close to needing the jumper leads!


Well-Known Member
Nice calculations there Millsy, but what about the effect of COLD WEATHER on batteries?

Your making your calculations on ISA conditions of 101.325 kPa's at Sea level (1013 mb to us Pilots) & 15 Deg C (They may have to change that :rolleyes:) :cool::D
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New Member
Then throw in CCA (Cold cranking amps) and RC (Reserve capacity) which are written on the top of your battery, and you'll never sleep at night:D:D:D


Active Member
Going back to my tech days (too long ago) I recall that some batteries can go into reverse polarity if allowed to discharge too low, problem is I can't remember which batteries they are.
If it is a lead acid what effect is a long charge gouing to haVE on a long charge, will it correct or bugger the cell.


4x4 Earth Contributer
Well tha battery died in the end, about 8 weeks ago. I had spent all Saturday packing the Patrol for a trip up to Birdsville and Innaminka. Looked like I was going to get away about 8 or 9pm. Was just going to get about 200km under the belt and sleep somewhere around Port Pirie or Port Germain.

All set to go about 9pm. Turned the key - flat battery! Still wanted to go. Rang up RAA to bring a new 4x4 battery. Told them the type of vehicle. About 10pm they arrive - with the wrong battery - too small. He leaves in search of the one I need. Gets back about 10.45 with the correct one - $230 - and I am finally away. Slept just south of Port Pirie. Yay, I am on the road again!

So when I returned I looked up the Ebay and bought a little solar trickle charger from Hong Kong - about $25 delivered. Battery should be OK now between trips. I checked the voltage yesterday - about 12.8 volts. Then started the engine for the first time in about 5 or 6 weeks. No probs. Not going to kill this one through neglect!


New Member
Great article on batteries 4x4, a lot of research has been done by yourself.

Can you advise me please what the 'N' rating of batteries means, for example N70


Active Member
Well tha battery died in the end, about 8 weeks ago.

Must be the season for it. Father in law has a number of batteries that are/have died, my main battery seems to be following along. A few months ago jumped in to go to town and it wound over slow but managed to start, then was fine until last week. It was either dead flat or barely able to turn the motor over. Gave it a charge and it was dead next morning. Then it's been fine again. Seriously hoping it's the battery anyway and not a starter deciding to go all finicky on me. Battery was sitting on 11.7 volts when it barely turned over.


New Member
Excellent Information and I do love the technical issues discussed here. I am new to the forum so I apologise in advance if this is not the right place but I will take this chance to dumb things down a little.
I did look at the dual battery system section but this is not really related. I have recently installed a red arc BCDC20 and an Exide ED5 as the Aux Battery. Since the start of the cold weather my Main Battery, which was in the vehicle when I bought it last year is very sluggish and looks like it will give up on me soon. It is a Century N70ZZL.
Can I have it charge to clean the plates and replace electrolytes somewhere or should I replace it. And if so do I match the deep Cycle ED5 (which I get at a reasonable price) or do I replace with another Century N70ZZ or other?
The Specs didn’t really Mean Much to me sorry but here they are
CCA @ -18°c:760
RC @ 25°c:185
Weight (kg):22.50
CCA 480
RC 135


Well-Known Member
Looking at those specifications I think the N70 would be the only choice.

For reliability I personally would go for a new battery rather than try to rejuvenate the old one but if you were to mess around with it you might get another month or two out of it but would you really trust it?

my 2 pence for what it's worth?