Actually, battery makers rate their battery life for all DOD levels, not just one and not just 50%.
The mistake that is made is to count cycles as representing the life of a battery. It does not. This is a completely inappropriate method of comparing the effects of DOD.
If you calculate the actual life in Ah at various DODs you will find that the variation between 20% DOD and 80% DOD is relatively small.
Please show us some manufactures (not retailers) advise proclaiming the 50% DOD recommendation.
Cheers,
Peter

Just in case you can't find some manufacturer's data, here is some from Fullriver (a premium priced AGM).

Aaahh, you say, that proves it.

Well let's look more closely.

At 50% DOD the battery will cycle about 650 times x 50Ah (for a 100Ah battery) = 32,500Ah total life.

At 70% DOD the battery will cycle about 450 times x 70Ah per cycle = 31,500Ah total life.

At 100% DOD (for EVERY cycle) the battery will cycle about280 times x 100Ah per cycle = 28,000Ah total life.

This clearly shows that there is no "cliff" that the battery suddenly falls over if it is subjected to deep discharges, there is a moderate loss in total life.

Fullriver numbers, not mine.

What must also be considered is that if you choose to discharge to (say) 30% instead of 60% on a regular basis (and this is a fair and reasonable choice) then you need to double the weight of batteries that you carry and double the dollars that you need to spend (but you need to spend it less often).

Cheers,

Peter

Looking at Victron AGM 400 x 80% & 600 x 50% you have more total AH draining the batteries further.

To power my 28L fridge at 15ah per 24 hours (4 x 26ah) at least I can go 6 days of inclement weather. A so called lithium at half the capacity gives me 3 days.

2 x 26ah lithium will not run my fridge for 6 days.

Hi 

I agree with the last couple of posts. There is disinformation about lithium equivalent capacity. BUT if you need Y Ahrs of capacity and you have a battery that has less it will run out, that is for sure.  If you have more LA capacity it will continue.

I see on one site that they claim 100Ahr of lithium is equal to 3x LA capacity ???? BS. But I am not anti Lithium and indeed own some that I use. But the price is too high so far and the cheapies now on offer are unknown quality and lasting ability. Not being a gambler I am sticking with LA till the facts are clear that I will be better off. 

Recently I bought a lithium battery for my motor bike(from a known quality seller). The usual small LA bike batteries are crap quality and as I ride infrequently I usually need to jump start to get it going(EFI). So I bought a cheaper Lithium battery of half the Ahr rating but the same CCA and size. It works well so far, as all it needs to do is supply the initial starter umph, several times possibly, and it goes. The LA battery would not do that after sitting for some weeks. So horses for courses ! The weight of it is so low that I suspect it is just two x four power tool style batteries with a BMS in a battery shaped box. It suits that job but but would not run the lights long after the engine stalls if they did not switch off. 

Jaahn   

Peter your "moderate" loss of life between 50% and 100% discharge is actually 67%, I don't see this as moderate.

Alan

Gravy73 wrote:

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Peter

A full analysis of your existing system and how deep your pockets are will determine what batteries to purchase as replacements. I am gathering your existing charging hardware is not Lithium compatible therefore you need to factor in the costs of replacements if you change from AGM or Float batteries.

Hopefully your existing charging hardware was selected to provide the correct charging current for your existing batteries. New technology provides the ability to program the charge current and also the charging regime for the type of battery connected, something that also has to be budgeted for if you alter the type and capacity of your existing batteries.

I wont raise the issue of the effectiveness of the two types of solar regulators, just to say there are misleading claims about and once again budget ramifications.

When you make your decision, if you want maximum performance and longevity research the manufacturers specs and ensure your charging current and DOD match that criterion.

Graeme

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 Hi Graeme, 

I have had a very busy Birthday buying and starting to replace my caravan house battery after a weekend of reading and learnings including doing the sums.

All will be revealed in the next day or so. 

Thank you All.

This is how our system in the 2012 secondhand caravan developed.

First in 2016 we had 340 watts of solar fitted.

Next a secondhand 2013 85 amp blue battery was added to compliment the orignal 100 amp battery.

This combination has worked brilliantly for 4 years.

We are very light users of power, once in 4 years I watched 2 dvds, 2 hours of the tv sometimes, we showery of a daytime when the sun is out, our frig runs on gas. We have gone months without using a 240 volt power  point.

We are campers with a aluminium mobile tent.

Hi All.

This is the end result, the system is a budget system using one 110 amp battery only being recharged by 340 watts of fixed solar panels.

In the tub of our ute to back the system up is another 90 amp battery, main reason it is there is to power the portable frig on day trips but can through a anderson plug back the caravan battery up for recharging.

Having a 3 way frig which runs only on gas when away home, led lights, using the waterpump in daylight hours only. We would ues only 12 amps from sunset and 8 amps near sunrise.

If I am right and we only need the one battery, Oone of the side benefits is 35 kilograms of weight saving.

Thanking everyone for their thoughts, Peter for dropping the hint for the battery guy at Arana hills not far from home and a very good price for batteries.

Now I am hoping for a minium 4 trouble free years.

3 weeks on the road update on our new 110 amp battery system.

So far so go, my prediction is that a 110 amp battery is all we need for our 12 volt electrical usage being recharged via 340 watts of solar on the roof is holding up good and working well.

Using led lights of a night from about 6pm on and the tv for a couple of hours, battery showing on Voltech regulator 12.6 volts at 5am in the morning the lowest seen in all 21 days of freedom camping. The weather up here in mid north Qld has been mostly sunshine with some light run and the odd day of overcast weather.

Very happy about loosing 35 kgs weight from the caravan and now running under weight, the cost saving of a second battery was good also.

Once again thank you Peter for your encouragement and the name of your battery source, time will only tell now how good the battery is.

Ps. To Craig, the battery is in a open top battery box mounted on the chassis under the floor outside the caravan. We do not want a bang.

November 2020

42 days away from home in Brisbane to far as Prospine with a mixture of camping options but mostly off grid.

Our system 110 amp battery being recharged by 340 watts of solar worked great.

Most cooking is done via gas, along with the refrigerator also running on gas.

A awesome 6 weeks away, bring on the next short term adventure.

Stewart wrote:

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Glad to hear it all went well we only have 1 battery and so far has worked great for our needs. Cheers Stewart

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 Thank you for the encouragement.