Battery Issues

Remember any state of charge readings need to be with the battery in a resting state and at a known and corrected temperature.

If the battery is under charge or under load the state of charge readings will be misleading to say the least......for any sort of meaning the battery needs to be rested at least an hour before measurement...no load no charge...for real accuracy think in terms of 4 pluss hours.

remember a battery is not a bucket and state of charge by measuring voltage is an estimation.

Also temperature has a great influence on battery performance and measurement.

Lead acid batteries are happiest at arround 25C.....higher they suffer from life shoteninmg effects, below that their capacity to deliver drops rapidly till arround 0C that will typically produce bugger all.

If you want to get some sort of idea of these influences, you need to go to one of the better battery manufacturer sites that show a full spec seet for their batteries ( not most car battery sites).
There you should see curves for state of charge corrected for temperature, battery capacity V temperature and a whole pile of other stuff.


You have a bank of 4 batteries..are they 4 x 12 volt batteries all in paralell or are they 4 x 6 volt batteries in series paralell.

either way, from time to time it is wise to seperate the batteries and apply an "equalising" charge and check the condition of the batteries individually.

You can do some basic tests with a decent voltmeter....but for anything realy meaningfull you need to test the batteries under load with some sort of loading battery tester like a battery analiser or a carbon pile ammeter.

I realise most people don't have these lying arround.....but most good battery shops should have them on hand.


ONE big trap with battery banks is wiring them all from one end of the bank......even though the connecting straps are heavy, the battery nearest the lead in will do most of the work and have a shorter life than the rest.

so it is wise to wire positive from one end of the bank and negative fromthe other end of the bank....with a 2 battery bank it more or less stops there.

if you have 4 batteries in paralell it is wise to rotate the batteries from time to time inners to outers.

paralall battery banks most certainly need attention and maintenance if anything other than a short life is to be expected.

Remember the basic design life span of a lead acid battery is two years.......improved technolgy can extend this quite a bit as can carefull attention.....but the basic design life span remains.

remember also..with apprpriate abuse the life of a typical battery can be reduced from up to 5 years to a matter of weeks.

cheers

Hi Humpback ,just a thought ,maybe a dc to dc charger will help out ,it seems as though you are not getting the amount of charge to fully charge your batteries ,and sooner rather than later your batteries will fail .You can get one that will accept solar as well as alternator ,and boost the charge ,that deep cycle like
Bigred

sorry...but here we go with this whole " fully charged & DC to DC charger" thing again.

Quote
Last night went to bed batteries were reading 12.8......

Now even without having complete controll of how the SOC is measured....the solar charging is obviouly complete for the day..( unless the OP went to bed at 5pm) and consulting the SOC table above....the batteries look fully charged to me.

it is more likley that there are issue of

errors in measurement of the SOC under load in the morning

There is capacity reduction in the batteries due to age or managment

There is self discharge in the battereies due to age or managment.

The above will almost certainly be compounded by cell balance issues within the bank.

cheers

Humpback,

I agree with Bantam on all points in his follow-up 820914 above, except maybe the first line :-), but that's not the issue.

The accuracy of battery monitors can drift, especially in the amp-hour counting area, and they need an occasional re-set.

More importantly, as your batteries age and drop in performance, some of the parameters used in the battery monitor are no longer correct for the condition of the battery. eg Peukerts constant (if you battery monitor accounts for that), and charge efficiency. A small error in Peukerts can result in a significant error in the amp-hours calculated by the monitor, especially if you're pulling occasional high currents, eg by running 240V appliances off an inverter.

An error in charge efficiency can have the monitor showing more amp-hours going into the battery than is actually occurring, so it reads 100% before the battery is charged.

But to me the voltages and behaviour you described in your opening post suggests that your batteries are on the way out.

If it turns out your batteries are stuffed, may I suggest you consider changing over to Lithium batteries. If you buy the same amp-hours in lithium as you have in your lead-acids, you will have twice the useable capacity, half the weight, a little over half the size, no sulphation, much reduced charging time. If you want the same useable amp-hours as you have now (200-ish based on the 50% rule), then the lithium pack will be even smaller and lighter.

In a caravan application you'll get over 3000 cycles, maybe up to 7000 and a calendar life of 10 years or more. Initial cost for the same useable amp-hours is about double, but they'll last at least three times as long so overall cost of ownership is way less.

Depending on the brand of battery you buy, if you have quality lead-acid chargers and solar regulators the lead-acid charging profile in them will be suitable. That will keep your costs down, though chargers with a lithium profile are preferred.

Cheers

Thankyou to everybody who replied great technical feedback very much appreciated,gave me alot to think about regarding new batteries , also when i can i will get them load tested.
Cheers
Humpback