Battery problem unexplained.

Was using a Cobra 105ah deepcycle/cranking battery too run the fridges charge detector batteries etc.
The last trip in 2013 found it would run the fridges all day while the solar was topping it up, come the night it would be dead within a couple of hours after dark.
Got home took it down to Battery World and their tong test came back positive?
Took it home trickle charged it in the shed over summer and the voltage hovered around 13V.
Getting prepared I hooked up my old 39L Engel to give it a test, within 3 hours it had stopped on low voltage.
Took the battery back to the experts and they told me it was in perfect working order and that there must be a heavy drain dragging the battery down.
Thinking the worst that my old Engel may be the culprit.
At home the c-tek battery charger was hooked to it for three days to go through a recovery cycle.
Next trial I soldered a couple of wires to a tail light globe and left that burning, about 4 hours later once again the battery was down.
Fitted the battery back in the ute and took it to the shop. The attendant came out with all their checking gear and I turned both fridges on., while we stood there you could see the voltage dropping off very rapidly even though the solar was putting in 2.5amps.
A tong test on cable running to accessories showed a 6 amp draw down which was consistent with two running Engels.
The long and the short of it I bought a new battery, left the ute in the sun to enable solar charge until dark. This morning both fridges still running, one on freeze (-7°C) the other on fridge (+3°C)

Any battery gurus out there who can explain why a battery that passed all the load tests at the shop failed to perform?

Cheers
Peter

hi pete
maybe it would depend on the battery tester they were using or the operator may have imputed the wrong battery cranking amps...

load testing depends on the machine testing the battery and if the battery was discharged then it would have taken at least 15-20mins to load test..

deep cycle batteries have a mind of their own sometimes...

regards
oneday

hi Peter,
really depends on the type of battery tester as Ray said, been a while since my auto elec days but we used to use a battery tester with a carbon pile in it, adjust it to suit the battery and watch the meter and electrolyte for bubbling, its harsh on the battery but you soon find the weak cell, the tong tester even sounds like its a token test unit only.

cheers
Darren

Did the same with my 100Ahr Rita AGM.....was tested at local Auto Elects in Kal....400Amps and holding...yet by 10pm it was all over rover. No probs during the day on the panel.
Decided to swap out my starter battery with it...stuck the truck into 1st gear and crank...i got about 2-3mtrs...game over.

Once their spent...their spent...no amount of rejuvenation helped.

Opted for a more expensive Chinese made battery...Fullriver....this is season two and holding strong so far.

Have you ever noted, if you look after your gear it lets you down, yet those who know no better, get an endless run.?  
Iv seen some setups that beckon disbelief, by the laws of physics they should not be running...yet live past some setups with correct thought.??

Peter,
You have a perfectly good shed light battery that will probably last years running 12v garden lights with a super-cheap 300mah solar charger costing $15. Put it to work. 

These sort of problems bug me big time, it would seem the battery shops need to lift the game in diagnosing problems or many are going to be caught out going bush with a "good" battery that is going to let them down miles from from help.
Narrawa,
Spot on mate, it is already out in the shed, trickled 24/7 by a regulated 400ma mini solar.
Will power my 12V man cave experiments and projects.

Cheers

Hi Nightjar

Rechargeable batteries have battery life which is calculated on the number of times the battery is drained and recharged. This is called a duty cycle and a battery and most cases are calculated at 80% drain of your battery. So puttiing it in simple terms a 120ah battery could be recharged 200 time at a 80% drain, after which the battery performance will deteriorate (not hold the charge as long) but this can vary by various factors such as how much drain battery capacity ect. This is how it was explained by a battery supplier at our power station. In your case this sounds like what has happened as I don't know how old the battery is and how much you have put it through the duty cycle. Hope this helps.

One thing is any battery deep cycle or not it is not recommended to go over the 80% drain as this will shorten the life considerably. Regards Ian

Thanks Ian,
My concern is not the fact the battery failed it is, if I didn't know better and relied on the retailer our trip away would have got off to a bad start having to drive back into the nearest town to buy a new battery.
Gave the set up another test run yesterday.
The new 105AH regulated charged with a roof mounted solar running a 60L (fridge) & 39L (freezer) Engel, for the exercise and the digital readout had actually increased a few points at end of test.     
With my old yellow that is run as a freezer the dial is turned back about one notch and doesn't run continuously but maintains -5/-7°C. There is about a fortnights frozen meat in there as is then turned off and the next fortnight we rely on the Engel combo and the van freezer (gas). This set up gives us a month away with the occasional run into town for a few consumables.

Hi Nightjar

What size is your solar set up as you mentioned on the roof. Just curious as you need to have enough current from solar to meet draw from fridge/freezer plus replacement of charge used at night on battery.

I have 120ah gel cell setup and 220w solar set up which I run a Engel 40l as a freezer and Waeco 50l as fridge. Both units draw about 4 amps when running (cycle as you mention), my solar set up is putting out about 12amps so there is enough to run the units during the day and enough to top the batteries up between 12-2 each day. Only back the units down if I get 2 or more days of cloud, and usually do this on a months stint.

Regards Ian

Morning Ian,
Have a permanent 64W Solar on roof of ute, when we drive out each morning I flick the switch on the solenoid to connect the vehicle dual system to the fridge battery so the alternator can put in a few amps. When we get to where we are going to swing a portable foldup 120W Solar is plugged into the system via anderson plug to keep the fridges going.
When we come back to the ute for lunch the portable is relocated to get the best sun angle.
If it is a bright sunny day we arrive back at the camp with the battery still full ready for the night ahead.
If there has been consecutive cloudy days occasionally the gen set is fired up and few amps pumped in using the ctek charger.
Anyway all good now and we are closing in to getting away for our first trip for the year.
Hasn't been any problems until the battery first mentioned in post acted up.
As a rule the vehicle and solar batteries usually live approx 3 to 4 years.

Cheers
Peter

Hi Nightjar

Yes you have it covered well I hope all goes well for your trip and hoping you find a few nice nuggets to make it all the better. I'll be heading out Monday but only for 9 days due to my old vehicle having to be put down with bad case of rust in the chasis and will have to go with a mate.

Cheers Ian