Member Since: 12 Oct 2012
Location: Hampshire
Posts: 329
Battery performance - measured
Not sure if this is useful or interesting to others, just putting the info out there...
I've owned my 55 D3 for nearly a year, and checking through the (extensive) LR history, I can't find any mention of the battery ever having been replaced. since the battery fitted is a gen. parts one, and I couldn't find any date code marked on it, I decided that changing it before winter would be a wise precaution.
Thanks to Boringoldgit and AF, the financial bit wasn't as painful as it could be, and last weekend I swapped out the battery.
Since I have the kit available, I decided to test the old battery to see if I'd really made a wise investment...
Click image to enlarge
Fairly standard battery test, discharge at 4.5A, intended to take 20h to flatten the battery to 10.5V
Result, the battery lasted 17h, so 76Ah, and about 80% of it's stated capacity. Not too shabby (I've seen brand new Optimas fail to hit 90% of stated capacity) and certainly not needing replacement.
I've since found the number 2810 stamped into the battery -ve terminal, so possibly it's only 3 years old.
So I'm unnecessarily out a pile of cash , but I have the peace of mind a new battery brings to those short on glowplugs, and I have a new jump-pack battery for the workshop
Swings and roundabouts...
25th Oct 2013 1:57 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi epninety and going on that graph, your battery reached it’s 20% discharged state at about 10 to 10.5 hours into the test.
This means your battery should have provided about 70 amperes at that point but by the graph, you were only capable of obtaining about 50 amperes so your battery was down roughly 30+% on it’s original capacity.
Also, while you can safely discharge an Optima down to 0% SoC or 10.5v, you can not discharger any normal deep cycle battery below 20%, or 11.58v without shortening it’s operating life span and it’s an NO-NO taking a cranking battery below 40% SoC or 11.9v, even for testing sake.
Your old battery would still make a good emergency jump start battery because the CCA of a battery does not start to degrade until the battery’s capacity falls below 40%.
And a tip for you, -ve is an electronic schematics term and not an auto electrical term.
-ve actually means a voltage below zero and this is something that should never occur in an automotive electrical system.2008 TDV8 RR Lux + 2009 D4 2.7
27th Oct 2013 7:39 am
epninety
Member Since: 12 Oct 2012
Location: Hampshire
Posts: 329
Actually, from experience of several hundred, you can't discharge an Optima (either cranking or deep cycle) down to 10.5V repeatedly without impacting service life either.
Testing does not have to be non-destructive, as far as I can tell both the SAE and BCI battery tests discharge to the end point 10.5V for measurement of RC (SAE) or Ah (BCI). I'm not shortening the service life of the battery because it's already completed its service life. You'll notice I didn't test the new battery?
That said, I should have mentioned the commented this isn't a good thing to do to a lead-acid battery that you care about.
Terminal voltage simply isn't a good method for determining State-of-Charge (SoC) unless you know the history. As you know, the terminal voltage will depend on recent history of charge/discharge/rest, and unless you have specific data for the battery design and knowledge of it's general condition, it leads to large innaccuracies in the predicted capacity.
'-ve' is simply lazy engineer typing for negative, I don't imagine it taxed the imagination of anyone who bothered to read that far down my post. There's a big '-' symbol cast into the battery next to one terminal that forms a good clue.
You might be confusing it with the common V- or Vee annotations used in circuit schematics?
27th Oct 2013 10:49 am
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi again epninety, the symbol ( - ) is the automotive symbol for negative and ( + ) the automotive symbol for positive and are the correct automotive notations and as you posted, they are on all automotive batteries.
There are no batteries marked with the symbols ( -ve ) or ( +ve ) for the very reason I posted earlier.
Also, carrying out a load test, as you described above, is an excellent way to determine the usable capacity of any lead acid battery, just never take them to 0%, 10.5v.2008 TDV8 RR Lux + 2009 D4 2.7
27th Oct 2013 12:20 pm
epninety
Member Since: 12 Oct 2012
Location: Hampshire
Posts: 329
A load test is a good method, I simply said that terminal voltage alone is not a good guide. It is something of an over-simplification.
For example, on the measured curve above, at around 11:00 the terminal voltage is measured at 11.4V, which using a typical curve would indicate around 15% capacity remaining.
At 15:00, the terminal voltage hits 10.5V and the load is removed. The battery is now at 0% capacity by your lights.
At 17:00, the terminal voltage is again 11.4V. No charging has taken place. The battery has simply rested.
So which is correct? It is generally considered that terminal voltage is a guide to battery capacity of a healthy battery, only after a long (several hours) rest period. So at the completion of my testing, the battery has a remaining 15% capacity, and therefore the battery is pretty much bang on 90Ah total capacity.
In fact its not, because I didn't follow the full test protocol, I didn't precharge in the prescribed manner, I didn't stabilise cell temperature, etc. etc.. I didn't do that for several reasons, the main one being that it's simply not that important. I'm far from the only owner considering a 'peace of mind' battery change at this time of year - I've not seen any published real-world data for performance degradation that I could believe in. Maybe this info is useful to other owners, if not, simply move on.
EDIT : Re-reading the above, it perhaps comes over as a bit argumentative, it's not intended to be. Battery performance is a very complex subject, and a lot of people much cleverer than me are spending a lot of research money trying to find a reliable method of measuring it.
27th Oct 2013 2:25 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8216
I'm keeping out of this one It can when others can't,
It will when others won't,
It goes where others don't.
27th Oct 2013 8:25 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi again epninety, correct me here if I am wrong but you don’t seem to have had much to do with lead acid batteries.
You keep referring to having to know the condition of the battery and then you referred to how the battery voltage settled up to a higher reading.
You are using two totally different types of terminal voltage readings to ascertain the SoC of a battery.
Your test is the best way for anyone to determine the actual Ah capacity of any lead acid battery and the chart below can be used while load testing a lead acid battery, and providing the load does not exceed 5% of the battery’s total capacity you will get a very accurate indication of a battery’s actual Ah, so your 4.5 amp load was the perfect testing load.
When carrying out a loaded battery test like you did, you do not need to know the condition of the battery or it’s history, in the first place. The only thing you need to know is whether the battery is fully charged or not, before the test is started.
As to the rest of your claim that you need to know anything else about the battery, this would be the case if you were using an OPEN CIRCUIT voltage measurement to try to determine the Ah capacity of a battery.
The problem with using an OPEN CIRCUIT voltage test is that, as you have stated, you need to now the exact condition of the battery and it’s history, PLUS the battery must have been in a No-Load/No-Charge state for at least 24 hours being able to get an accurate indication of the battery’s Ah, based on it’s terminal voltage.
The problem with OPEN CIRCUIT voltage tests is that while the voltage reading may indicate a given battery is fully charged, but it is a common situation where once you put a load on the battery, even a small load like that in your test, the battery terminal voltage drops rapidly, now indicating that the battery is actually stuffed.
OPEN CIRCUIT voltage readings are useless in RV situations and the voltage reading you got after the battery had the load removed are of no real use.
Where as, with using a known load to carry out a loaded battery test, you will not only know the exact Ah capacity of the battery by the time the battery is discharged down to it’s safe discharge level, 11.9v or 40% for a cranking battery and 11.58 or 20% for a deep cycle battery, but if the battery voltage drops to quickly while carrying out the test, you will have already determine the condition of the battery.
Last but not least, manufacturers establish the SAE and Ah of batteries by carrying out tests on batteries that are never going to be sold on and as such, it doesn’t matter if the battery is damaged during the test.
But for real world use, there is no reason to discharge any battery down to 0% or 10.5v when you can’t use the last 40% in a cranking battery or the last 20% in a deep cycle battery. So why test beyond these levels.
Click image to enlarge
2008 TDV8 RR Lux + 2009 D4 2.7
27th Oct 2013 9:03 pm
epninety
Member Since: 12 Oct 2012
Location: Hampshire
Posts: 329
If you're going to suggest I don't know what I'm doing, it's probably best not to follow it by re-stating most everything I said.
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, but I have the peace of mind a new battery brings to those short on glowplugs, and I have a new jump-pack battery for the workshop 
