WHAT IS KILLING MY AGM BATTERIES?

jat,
Another possible cause. Is the battery under the bonnet as AGM batteries don't like heat.

What sort of 12v fridge is it?
If a 3 way type then that will kill anything.

Where are the batteries situated. If under bonnet ie in HOT zone, the heat may be killing them.

Is all the cabling correct/suitably sized to allow for the batteries to actually get fully charged?

Are the battery terminals CLEAN and a good connection with the cable lugs,clamps?

Is the relay actually disconnecting the main battery?

Is the alternator faulty ie, one diode sick.
It is hard to believe the alternator is only 30 amps output. A 90 amp alternator with a blown diode, ie, an open circuit diode, immediately reduces the alternator output to 1/3 of it' total output, so a 30 amp maximum charge would indicate a 90 amp alternator ( which is what I would expect it to have) really does have a DUD diode and that may be contributing to your problem. If a Valeo alt then it is even more highly likely.

Just a few things to ponder. It may point you in the right direction.

Have you batteries "died" as in stuffed and can't be revived...... or are they flat flat flat.

1) What have you done to determine the above.

2) Have you had the batteries charged at a place like a a battery place, auto elec or local mechanic to see if they can charge them OK.

The chances of having multiple failures in a short period of time is odd.

Who installed all your aux battery gear?

I have a camper on the back of my landcruiser so might be similar setup. In the camper I have 2 x agm batteries and suffered a similar problem with them going flat. How I fix this problem now is to...

1. Change all the leads to accessories like fridges to 6mm2 leads. Cost a bit but worth it.- ordered the cable from ABR Sidewinder who is a forum business member.
2. Bought a DC to DC charger - made all the difference for the charge coming from the car and the Solar panels. The voltage drop from alternator to camper batteries seemed to be enough to effect the charging. This was probably the biggest one.
3. Bought a 'charging chip' which goes inline to the car alternator and ups the car charge from 13.4 to 13.9. It seems new cars deliberately have a lower volt charge to help with ??? economy, pollution control ... who knows what. This also seem to help especially with the under bonnet dual battery system which is separate to the the camper 2 x batteries. (so I have 4 x batteries all up)

Before I could barely last 3 days before I had flat batteries. Now I have been 4 weeks on the road and not a problem. Also I got rid of the Waeco fridges. They draw a lot.

Cheers

Serendipity

"3. Relay - Nevara charges upto 16v my vans Altinator 30Amps. Merc sprinter. I have seen 15V in display."

What was the ambient temperatures when you noted those voltages, those are quite high charge voltages and I would only expect to see those out of an alternator in a very cool climate. You wrote the batteries died after 5 to 6 days of 6 hours duration drive times, if the ambient temperature was above 15C I wouldn't be surprised at all that the batteries died.

Hi Jat G
A few things to check.
1)Alternator voltage at car batt then house batts.
2)Is the wiring heavy enough from the alternator to the house batts?
3)Is the alternator seeing the house batts?(a problem with modern electronic alternators)
4)Your batt charger is under powered to charge your battery pack.Even know on the box it says it is in its range that is crap.The rule of thumb is what ever your battery capacity your charger should be at least 10% of your battery pack.EG 2x105amp batts=210amps.Minuim size charger 20-25 amps.Your battery charger must be in a well ventelated area,preferrably cool as to not over heat.The hotter your charger gets it lowers its out put to protect its self from over heating.
5).1 of an amp with nothing working is standard.
If i had to stab in the dark i would guess your under powered charger is the problem.A 10amp charger trying to charge 210 amp battery pack would be working its ring off.So it would get hot pretty quick and then lower its out put to protect its self so your batterys would never be fully charged.
Good luck with your problem.

Low voltage cutoff/alarm in the morning shows that the battery available capacity wasn't adequate to meet the overnight discharge. Just analyse that for a moment. Either more load than you thought or under-charged to start with.

Reading (presumed the max) of 25A load? Where is it going? The fridge? Is that "6 to 8 Amps" really Amps or Amp-hours? Is it a 3-way? If so, the current draw on DC is CONTINUOUS. Scary!

The solar charger - are you sure (i.e. have you checked) that there is no discharge through it after sundown? Does the solar reg interfere with other charging methods? How is it interfaced to the rest of the system?

Alternator 30A - is that for real? Nameplate or measured? (In 1970 I had a small Fiat which had a 55A unit). If that's what the nameplate - or manufacturer - states then chuck it away quick smart and get a real one. If measured, it definitely sounds faulty and that would tie in with failure after several "long-enough" driving days.

The "relay" used to parallel the AGM's with the cranking battery and alternator - has it been tested? Where are the AGM's located? What does the manufacturer recommend as a charge regime and in particular the float voltage?

Two sets in that time says clearly there is a problem in your arrangement. It *could* be overcharging, or it could be under-charging. But until you are able to monitor voltage with some precision at the AGM's while on the road the picture will not become clear. (I'm unable to include a pic of my setup but it is an accurate voltmeter with a selector switch mounted under-dash so I can monitor main or aux battery voltage on-road to 10mV resolution. That would allow quick determination of over-charge or under-charge and whether the parallelling relay/device is functioning properly). Either that or MEASURE (not estimate or "calculate") current in various parts of the system to see what is flowing where.

Some time ago I invested $50 in a Chinese tong-type meter with DC current capability (many don't have that feature) including a 40A max scale. That has come in handy in sorting several other vehicles' issues. While any competent auto-sparky could sort your system, there is a feeling of satisfaction doing it yourself with guidance, as well as $$$ to be saved.

Your Century AGM batteries have a maximum initial charge current of around 25 amps.
Your Mercedes Alternator is actually between 115A and 150A max current.
Your regulated voltage is high at 15V.
Put those three things together and you have dried out your AGMs by exceeding the allowed charge current. Little wonder they died.

By using a simple relay as an isolator, so you are delivering full voltage and unrestricted current to the AGM batteries.

You need a device to limit the charge current to those batteries. A 20A DC-DC charger would do the trick. With 2 batteries, maybe a 30A, but I wouldn't use a 40A.

I've got a number of top-of-the-wozza Exide calcium batteries (they come with 48 mth warranty), Marshall "commercial 4x4" batteries, and Supercharge Gold batteries - and every one of them has a decal on top, that clearly states "MAXIMUM CHARGE VOLTAGE - 14.8V".

I think you need to do something about ensuring the voltage output of your alternators is limited to 14.8V.

The advice about poor electrical contacts creating resistance and thus raising voltage is crucial advice.
Check that often-overlooked very important item - the earth strap between body and engine - for cleanliness and security of contacts.

Cheers, Ron.

Now to summarise.

Maximum initial charge rate not limited to keep within spec.
Charge voltage too high.
Temperature may be a factor....everything about every battery suffers above 25C.
Overnight current draw may be more than visioned and thus cycle depth deeper than expected.

All of the above will cause some deteroiration over time, resulting in reduced capacity.

Reduced capacity..more vunerable battery.


NOW
because you have two batteries in paralell.

Identical batteries..good

BUT..exactly how are they wired.

Do the main connection cables both come to one battery and then paralelled to the second?
If so this can cause one battery to work harder than the other......it may only seem to be a small extra resistance...but it can make a big difference.

Best to wire the batteries in paralell as usual..then connect the positive lead to one battery and the negative lead to the other.

What can happen is one battery is stressed and fails and takes the other with it.

Not saying this is the whole cause but it is a proven problem in paralelled batteries...

All of the issues mentiond may not be a cause on their own......but compounded they may be spelling rapid death.

Un when you replace your batteries....um maybe not Century and maybe not AGM.

cheers

Wow thats a lot to think about. Lets see if I can cover most questions here even with alzeheimia brain waves.

Batteries are inside car not under bonnet.

Solar reg. has Tempurature sensor direct on bat. Displays in the 6 months round 18 deg. night colder down to 5 occasionaly.

Batteries show no sign of heat.
2 Batteries are wired - Neg to neg and pos to positive. A 100Amp cable which seems tiny to me but battery world meant it was totaly fine as batteries are only 15cm away.

My saying the Alternator was charging to 30Amps - was quoted to me by RV builder. BEEP! Wrong. Thanks.

Nevara relay connection wire is about 1cm thick brass, its dam thick and only 1\2 a meter away from starter battery which is located also in the car under passanger side floor.

Monitored via Multi meter direct on battery and on solar regulator display (Same reading)
All wire thicknesses are adiquate to accessories. I was very pedantic about that when building.

Fridge is a not 3 way. 12V compressor fridge - Draws up to 7 Amps whilst cooling only a few minutes at time, not per hour! Over 12 hours it will draw a "total"of 8 Amps (seen as load on display of solar regulator) not Amp hours.

1. I have booked it into Auto electrician wednesday. I will definatly get him to see what we can do regarding regulating voltage from Alternator and have him test it along with Nevara relay.

2. Just upgraded Charger to a projecta IC2500 with built in tempurature sensor today "TICK"

3. Also will disconect NEVARA before driving anywhere. If sunny 20amp solar panels do the job well.

After driving battery charger stopped charging when plugged into 240V quite quickly.
Is it ok to have solar regulator on all the time? Do batteries prefer rest time?

Hope I've covered most of it.

Thanks you all for your answers, your all really great. This would have to be the best forum!! I like U.

My son is a mechanic for Mercedes , he advised that he often replaces batteries at around 6 months on newer models due to their smart charging system not charging the original battery correctly. How old is your vehicle ????
Just a thought...

I wouldn't go down the DC/DC charger path just yet.

1st, I'd find out what the problem is.......and by the amount of replies, there are a few to investigate.

When you find the problem, a DC/DC MAY be the solution, but until you know, it may be a waste of money.

Possibly related to the original post. I have one of these 12v solar trickle panels that you plug into the sigarette lighter socket to maintain a battery . I had one on my boat battery but the battery still died after a few months . Testing the output this morning of this solar charger panel it came up as almost 24 volts in stead of 12 or 13 volts . This is surely a fault in the thing as that will destroy any 12 v battery?

Holly help needed!

Fully charged battery reading 13.7V I head off for the day. After running 25Amps of power, cut off switch was activated at 11.5V Max Tempurature - 24
The day before Voltage reached 12.2V - after useing 16Amps although 10Amps came back from solar panels.

To recall I bought new 2 x 100Ah "Full river" batteries 9 days ago.

I now go for anything up to 6 hours per day without mains power. 12V Fridge draws 6.9Amps max per hour and is the main drawer in those few hours. Solar panels 400Watt charge upto 20Ah if daylight and parked in the sun.

Every night l have mains power and nothing runs on 12V whilst battery charger brings batteries into float mode. 13.7V to recall I bought a new IC2500 projecta intelli charger with Tempurature sensor.

SOLAR REGULATOR Dingo 40/40 is set up to monitor everything.
Beginning each day at 12midnight.
Tempurature sensor and reading.
Max Volt
Min Volt
Measures all Power being used and put back (Amps)
Solar panels charge - in
Load drawn Out. External and Fridge via regulator.
History - upto 30 days.

I have an extra cut out relay 11.8V for external equiptment.
The fridge is connected to the load of dingo 40/40 directly, cut off is set for 11.5V

I have disconected Navra from car battery. So am not charging from car battery only from solar panels whilst driving.

Max Volatage since installing - 14.8 V most days I see 14.2 V max reading.

Now who would still believe that it's the batteries after exchanging them 3 times within 1 year.