The truth about battery life?

Submitted: Sunday, Jun 15, 2008 at 21:22
ThreadID: 58828 Views:2994 Replies:9 FollowUps:7
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Do we know the truth about the batteries we use or are we just passing on something we have heard along the way?
Studying the specs for my new 100ah AGM I submit the following for discussion.
The commonly accepted max recommended discharge for an AGM is 50%. Maintaining 100% charge capability of the battery, Specs state that the max cycles at 50% DOD is 300.
i.e 300x50ah = 15000 ah of useful charge. (500 days use at 30 ah per day)
However if we look at the specs for 100% DOD, we see that the max cycles is 205. i.e 205x100ah = 20500 ah of useful charge. (683 days at 30ah per day.) More than 30% longer life than if discharged to 50% DOD.!!!!! The figures are not much different for a battery capacity of 80%
Are we all fooling ourselves by thinking 50% DOD is best? or does the maker know best?

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Reply By: Member - Serg (VIC) - Sunday, Jun 15, 2008 at 21:35

Sunday, Jun 15, 2008 at 21:35
Very interesting and valid comments. I have not comparing those number for myself, but my brain tells me that it could be very very true that discharge battery deeper means less number of recharge cycles, but more energy pass through.

AnswerID: 310207

Reply By: Crackles - Sunday, Jun 15, 2008 at 22:03

Sunday, Jun 15, 2008 at 22:03
It's pretty simple Ian. I fit the biggest ah battery we can squeeze into the space. We run the fridge & lights as long as we need them to run & take little notice of the figures as we really don't care what the DOD is as in the field it can't be easily measured anyway. What's imortant is the drinks are cold & we're not sitting in the dark.
Are we fooling ourselves? No. Because according to your figures to get the additional 30% more power you'd lose 30% of the batteries life. (205 cycles V's 300)
Cheers Craig..................
AnswerID: 310216

Follow Up By: Ianw - Sunday, Jun 15, 2008 at 22:47

Sunday, Jun 15, 2008 at 22:47
This is what I'm saying! Forget the 50% rule and use the battery as it suits you! (And you actually get 30% MORE life out of your battery not less.) i.e. 205 cycles of 100 ah (20500 ahrs), as against 300 cycles of only 50 ah (15000 ahrs).
It's just that when someone asks advice about batteries heaps of people jump on here and quote the 50% rule as gospel, and without an argument against it , the whole thing gathers more than necessary credence.
FollowupID: 576251

Reply By: Member - Phillip S (WA) - Sunday, Jun 15, 2008 at 22:37

Sunday, Jun 15, 2008 at 22:37
GEE...I blokes and your fretting calculations!!!!!.....My last two batteries lasted four years and I traded them in for two new ones...hope to get four years out of them too,,,BUT if I don't, who cares...not me....while you blokes are figuring this and that and getting your nickers in a knot...I'm out there doing it with what I got and having fun...cya.
AnswerID: 310225

Reply By: Gronk - Sunday, Jun 15, 2008 at 22:42

Sunday, Jun 15, 2008 at 22:42
If for instance you had a battery in a CT and you used it every two weeks, then that would be 25 recharges a year......times 10years = 250 in theory it would last 20years......but in reality who keeps their CT for that long and who really cares either ??

Don't let them fall below 11.6V, abuse them a bit , recharge them properly, forget all the technical stuff and enjoy them for years to come..
AnswerID: 310228

Follow Up By: Ianw - Sunday, Jun 15, 2008 at 22:49

Sunday, Jun 15, 2008 at 22:49
Now you're talking!!
FollowupID: 576253

Follow Up By: Mainey (wa) - Monday, Jun 16, 2008 at 22:01

Monday, Jun 16, 2008 at 22:01
The simple maths scenario will never ever work with a 12v battery because there are just far too many possible variables involved.

One 'well known secret' is to recharge the battery as soon as it's been used, yes everyone already knows that, however I would never never never allow any of my batteries to go under 12 Volts, therefore my fridge is set to disconnect @ 12v.

I still have a 6yo Delkor DC that will still Crank a 2.4Lt Diesel, because it has never been over discharged, it's never been subject to sulphation, as it's never been below 12v in those 6 years.

In 'my opinion' (yes, I'm biased) only a correctly specified quality Solar power system can maintain the battery system to suit these conditions.

On some of my pictures on my 'members profile' it shows the fridge is running and the battery is still being charged @ 13 Volts, because the Solar system is actually running the fridge and also charging the battery at the same time.

Mainey . . .
FollowupID: 576435

Reply By: macbushy - Sunday, Jun 15, 2008 at 22:51

Sunday, Jun 15, 2008 at 22:51
I concur with most of the above,
Rule 1. Beer must be cold.
Rule 2. Charge when able
Rule 3. See rule 1.
Rule 4. If I have had several years out of an abused battery, and the beer has been cold, well worth the cost. (think about it....when it's 44C, and you are sitting on a beach, watching sun go down, surf rod is twitching, beer is cold, fridge is humming, who cares if you get 2 years or 4 years out of your battery.)
AnswerID: 310231

Follow Up By: Member -Dodger - Sunday, Jun 15, 2008 at 23:21

Sunday, Jun 15, 2008 at 23:21
My sentiments exactly.
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I used to have a handle on life, but it broke.

Cheers Dodg.

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FollowupID: 576261

Follow Up By: Member - Phillip S (WA) - Sunday, Jun 15, 2008 at 23:53

Sunday, Jun 15, 2008 at 23:53
That's it
FollowupID: 576266

Reply By: Member - Craig M (QLD) - Monday, Jun 16, 2008 at 07:09

Monday, Jun 16, 2008 at 07:09
Can't help but wonder if some non-battery owned reputable mob (ie Choice etc) has done the 'compare the battery' exercise?

I am currently trying to insert a battery up the fundamental orifice of a supplier who assured me that the battery he sold me was 'heavy duty' and 'much bigger than I really needed' and 'would last for years' This is after only 5 months.

I won't name the battery manufacturer for fear of starting a war of biblical proportions because I am sure that my problem is a dodgy unit/supplier rather than dodgy battery company

Does anyone know of such a comparison guide that is completley independent of battery shop charlatans?

AnswerID: 310249

Follow Up By: Mr Pointyhead - Monday, Jun 16, 2008 at 09:26

Monday, Jun 16, 2008 at 09:26
A friend once worked for a well known battery distributor. One of his jobs was to put the stickers on the batteries. The only difference between the normal batteries or heavy duty was the stickers. The new batteries would come in on a pallet and his boss would tell him if they needed more normal or heavy duty batteries, and he would apply the appropriate sticker. ..
FollowupID: 576304

Reply By: Vivid Adventures - Monday, Jun 16, 2008 at 08:32

Monday, Jun 16, 2008 at 08:32
Google Peukert... there are plenty of non-linear effects involved here and your calculations are pretty simplistic.

That said, your conclusion is probably not far from reality.

The makers know empirically. The makers make rule of thumb recommendations that are not directly related to their empirical findings for that particular battery - just general "good practice".

In practice you have your battery for a job.
You make compromises about space, capacity, etc., in selecting your battery.
Your travelling and camping (or whatever) conditions, don't always match the ideal.

The retailer has no way of knowing the detail of this - before, or after.
The warranties they put on them are just what they can get away with assuming that most consumers will use them in certain ways. Consequently you can take a battery back to them, and they will probably replace it within warranty because they can't prove abuse. I am happy to live with this.

I am a battery abuser. Perhaps it could be argued I am a battery retailer abuser but because they constantly recommend their products as good for what I do, I have no hesitation in using their warranties to the full extent.

Andrew taking back a Calcium-Calcium battery today.
AnswerID: 310268

Reply By: Member - Kiwi Kia - Monday, Jun 16, 2008 at 08:48

Monday, Jun 16, 2008 at 08:48
I have long held the view that you need to buy this type of product from a company that will provide GOOD service. You need to be able to get a 'no questions' replacement if you have problems during the expected service life. I find that it's better to buy a median value product and expect to throw it away say - every three years rather then pay heaps of dollars and shed tears when your super-dooper 'long-life' brand does not last any longer then the cheaper product.

AnswerID: 310272

Reply By: Member - Phil G (SA) - Monday, Jun 16, 2008 at 12:57

Monday, Jun 16, 2008 at 12:57
If a battery doesn't have at least a 2 year Aust-wide replacement warranty, then the manufacturer doesn't believe in their own product. That will pretty much limit your choice to brand-name wet cell cranking batteries.
AnswerID: 310313

Follow Up By: Mainey (wa) - Monday, Jun 16, 2008 at 22:15

Monday, Jun 16, 2008 at 22:15
However, remember when a *Cranking* battery is used as a "storage" or "house" battery (NOT a Cranking battery) the Warranty may NOT for the same time period and it may not even be covered at all if it is being used for a purpose other than that as the manufacturer has specified !!!

Mainey . . .
FollowupID: 576436

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