Battery Issues

Need some help from the tech people regarding free camping and the problems I'm having with my batteries.
The van I have has 4 x 105 deep cycle marine batteries + 5 x 85 watt solar panels on the roof, the batteries are coming up to 3 years of age.
I have two volt meters on board 1 digital and 1 in the solar control unit which read very similar.
I have LED lights through the van and have a 210lt compressor fridge that I have had tested and pulls 5amps.
Last night went to bed batteries were reading 12.8 woke up this morning and the volt meter was on 12, checked solar control unit and it read batteries 33%. Overnight temps are very mild.

During the day the solar control unit will read batteries 100% but when night falls the unit will drop to around 59% within the hour or so.

During the day batteries will read 27c but over night when it gets cooler they will drop to 10c, does this have any effect on batteries in the morning?

Generally do batteries need to be given a boost with the generator or should the solar panels be enough to keep them charged?

Regards Humpback
Back Expand Un-Read 0 Moderator

Reply By: Member - KBAD - Sunday, Jul 27, 2014 at 10:40

Sunday, Jul 27, 2014 at 10:40
Humpback given that the solar control unit is reading 100 % across the board during the day (I take that this is in referral to state of charge of batteries and not solar input) i would say that you have an issue with one or more batteries. The best way about it is to isolate the batteries and check them one at a time with a voltmeter if any are reading low i would say that it needs to be taken out and either conditioned or replaced.

AnswerID: 536667

Follow Up By: The Bantam - Sunday, Jul 27, 2014 at 20:59

Sunday, Jul 27, 2014 at 20:59
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 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.


FollowupID: 820905

Follow Up By: Member - Bigred13 - Sunday, Jul 27, 2014 at 21:25

Sunday, Jul 27, 2014 at 21:25
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
FollowupID: 820908

Follow Up By: The Bantam - Monday, Jul 28, 2014 at 06:46

Monday, Jul 28, 2014 at 06:46
sorry...but here we go with this whole " fully charged & DC to DC charger" thing again.

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.

FollowupID: 820914

Follow Up By: Member - Frank P (NSW) - Monday, Jul 28, 2014 at 11:25

Monday, Jul 28, 2014 at 11:25

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.


Lifetime Member
My Profile  My Blog  My Position  Send Message

FollowupID: 820930

Reply By: CSeaJay - Monday, Jul 28, 2014 at 15:58

Monday, Jul 28, 2014 at 15:58
Technical advice in responses received. May I add personal experience, (I have two same sized batteries with an 80 l fridge/freezer) that is a very large fridge you are running on two batteries. I am not surprised the time it lasts if you run it as (part) freezer
AnswerID: 536730

Follow Up By: humpback - Tuesday, Jul 29, 2014 at 19:55

Tuesday, Jul 29, 2014 at 19:55
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.
FollowupID: 821023

Sponsored Links