Charge rate differences ??

Tim,
Typically, it's to the contrary. Most AGM deep cycle batteries prefer a bulk charge current of 10 to 15 percent of their rated C20 capacity. So a 100 Ah battery would typically prefer a charge rate of 10 to 15 amps, 200Ah 20 to 30 amps, etc.

Of course, there are exceptions, so you need to ascertain from the battery data sheet or the manufacturer what the preferred rate is. Sometimes it's on a label on the battery case.

Wet batteries generally can accept higher charge rates but they may vent and depending on what's nearby and the environment, there may be corrosion issues as a result. Again, not always the case. I had a wet deep cycle 105Ah battery that required a max charge current of 11 amps - ie same as an equivalent AGM.

If you're not using a dc-dc charger then I'd try to find a deep cycle battery of any type that can accept the charging current of your vehicle alternator.

If you use 1 x 200Ah battery, if it drops a cell (which kills the battery) you've lost everything. If you use 2 x 100 batteries, then if you lose a cell in one battery, you still have half your capacity remaining.

Cheers

I would not consider using standard wet cell deep cycle batteries.
AGM type batteries are the safe way to go, especially in non-ventilated spaces.

Don't go for a cheaper solution or you may well regret your decision.

Better still, if you invest in a dc-dc smart charger for charging whilst driving, you will extend the useful life out of your batteries as they will receive a multi-stage charging process, without the risk of overcharging and shortening battery life.
This is also the case for on-board AC charging.

Moving to a single battery (if you can lift a 200Ah battery) will not give you much improvement either. Down the track, should one cell in one battery malfunction, the whole battery is useless. With two batteries, you can disconnect the faulty one and survive on one 100Ah battery for a period of time.

wet cells shouldn't be used where leaks could cause massive amount of damage to either chassis components or human body acid burns etc -IMHO

2nd ever tried to pickup and carry a 200ah battery before ?

a quick google search tells me they probably close to 40kg heading towards 60kg in some instances.

Know all the comms trailers built at my former employer were always smaller 100ah for lifting purposes, one retrofit came in with a single 200ah took 2 guys to lift and remove it only take one to remove and install a 100ah battery

Most 100ah typically give more ah than 100 referenced to around 115 to 120 ah so 2 x is higher than the nominal 200ah capacity gives

My statement is in fact correct for situations where charging of an auxiliary battery is involved.
When a dc-dc charger is not employed, the common solution is to use a vsr to provide some sort of protection to the starting battery.
The vsr will not enable full charging of an auxiliary battery bank and a shortened battery life is the result.

Tim F3
I have a 35amp hr AGM battery which I use (CPAP) whilst travelling. I just charge it thru a Cig lighter socket. I can normally use the AGM 3 times before I need to recharge it at SOC 60% when I start charging it I put the multi meter on it and it rarely accepts a charge over 13.3 v . But happily the AGM is 'full' at the end of the days run. However the Wet Cells regularly accept 14.2v when they are at SOC 60%.
No smart Alternator its a 2000 model Diesel Troopy no computers.

Jeff

Speed of recharge and charge acceptance in a battery is driven by heat. Heat is caused by the battery's internal resistance. Internal resistance is governed by the purity of the lead used in the construction of the battery.
Check the spec sheets for internal resistance figures and lead purity percentages and you'll get a fair idea of how it is going to recharge.
There is another level of chemistry to talk about as well, but that is the meat and potatos.
Generally speaking, the less you pay for the battery, the more expensive it will end up due to a compromised life span and poor performance. The more "expensive" batteries last longer and perform better and worked back, are always cheaper on a $ per year basis.
Lesson = don't skimp.
Saying vsr is as good is a dc charger is saying a 14.4v power supply is as good as a multi stage 240v charger - not true. Yes, a vsr often wins the bulk charge race, but a dc will often have 5 steps as opposed to being a one trick pony. Long term optima users such as myself will remember having to hook them up to a home charger once a month to prevent them getting a charge memory from alternator charging. We don't have to worry about that any more with dc charging. Each have their merits, but dc will maintain a battery better and keep it alive longer every time.

G'day Tim,
for better understanding of the matter, there's some charging 101 for you.

The speed of charging is governed by the voltage difference between source and battery.
Example:
Valternator - Vbattery = 1V
So we've got 1 Volt driving the charging current which now depends on circuit resistance which includes the battery's internal resistance (Ohm's Law applies).
For instance, a circuit resistance of 20 milli Ohms will result in 50 amps of current.

If a high charging rate is desired, the voltage difference has to be large which can be achieved by high alternator voltage, a low battery resting voltage or both.
That's why high rate batteries come with lower acid concentration which produces lower resting voltage.
For the battery to actually 'accept' a high rate, most of the charge needs to be stored near the surface of its electrodes, so we want to maximise the surface area, aka number of plates.

Problem with this, thinner plates come with thinner grids which don't retain the lead paste very well. Each cycle will see some shedding of active material which piles up at the bottom of the container, resulting in poor cycle life.

To work around this issue, the enhanced flooded battery (EFB) has been created in which a fleece separator between the plates retains the active mass better.

Then we've got VRLA AGM technology which offers good retention through compressed micro fibrous glass mats between the electrodes.
The other advantage is it enables gas transport between the electrodes so that hydrogen can recombine with oxygen which preserves the electrolyte.

Which battery type combines all of the above?
AGM technology for start/stop cars, predominantly coming out of Europe.

A couple of days ago I replaced an AGM start/stop battery, date stamped 2011, in a Touareg.
So these things are made to last.

hi
Tim F3
Charging all batteries is as per the maker suggest . You will be surprised at how different the battery makers are .

charge amps as a percent of there ah capacity
lead flooded 10% slow --20% fast
agm 15% slow -- 30% fast
The above is rule of thumb

Never have wet batteries venting to inside van

lets sumarise and address some of the points raised.

#1 and above all .. DO NOT believe or take at face value any of, the only partly founded, commonly held "truths" about batteries in particular AGM.

No matter what the "rule" is there is an AGM or other type of battery that proves the rule is false.

We must look at the detail and the manufacturers spec's

There is one reasonably well respected Chineese manufacturer of batteries that manufactures and sells the very same battery in three different forms.

AGM (with little or no free electrolite, all the electrolite is contained in the glass mats), Sealed lead acid ( not claimed to be AGM, which is partly filled with electrolite) and as a Flooded wet cell sealed battery.

All three batteries use the same case, plate structure and materials .... all that varies is the amount of electrolite and some variation in electrolite formular.

The Australian distributor was zipped a few years ago by the ACCC, because there was a batch of partly filled batteries that came into the country and where sold as AGM when they technically where not ..... nothing wrong with the batteries as such , they just where not as discribed.

That manufacturer also builds a range of batteries with differing performance, they make a low current AGM battery that has a maximum initial charge rate of around 20 amps for a 100AH battery ( this battery also has poor high temperature tolerance) they also make a nearly identical range of batteries that has a much higher Maximum initial charge rate around the 50 amps for a 100AH battery and a full blown Cranking battery that makes a lie of every rule about AGM you have ever been told.
This cranking AGM can be charged very hard, its Cold Cranking Amps will make pretty much any conventional battery look sad and they have high temperature tolerance for under bonnet applications.

Generalisations about batteries can be very misleading .... you must consider each battery on it's merits and look at the specifcations.

2/ Do not confuse "Maximum Initial Charge Current" and "Charge Acceptance".

Maximum charge rate is determined by several factors, but it is the limit of how much charge current the battery will tolerate without damage.

Charge acceptance is how much charge the battery will accept and continue to accept.
Two hypothetical batteries ...... both at the same state of charge and condition, both at the same charge voltage and both starting at the same initial charge rate ... all equal to save confusion.

The battery with better "Charge Acceptance" will continue to accept charge at a higher rate as the batteries state of charge rises. ....... it will reach a higher state of charge faster from a given charging source.

The fact that the battery with better charge acceptace MAY ( but not always) achieve higher charge current from a given charge voltage is another issue .... not a seperate issue but another issue.

Charge acceptance is not exclusivly tied to internal resistance ... but it is related.

Saying that Charge acceptance is governed by heat and lead purity is a bit of a stretch.

Saying that charge acceptance and a number of other things are directly related to plate thickness is also a bit of a stretch.
Manufacturers are doing some clever things with plate structures and battery metallurgy and chemistry that make the old plate thickness arguments less and less valid ... not invalid , but less and less of a factor.

One thing that most definitely does influence Charge acceptance in all batteries is, ..... age and condition.

As batteries suffer age and abuse, their charge acceptance suffers ... and badly.
Sometimes this can be recovered a little with good treatment, but all batteries will eventually die from the same things that cause this.

I have had a not fully discharged, mildly neglected N70 marine battery take 3 days to reach full charge on a good 5 amp multistage charger, where a healthy example would recharge in 24 hours from neatly stone flat.

That battery did recover reasonably to live another year in light use.

3/... as for the 200Ah battery .... yeh hell ya don't want to be lifting that ..... most applications that 12V 200AH capacity will be made up of two batteries.
Look at trucks, busses, golf buggies and most small to medium earth moving ...... pretty much all broken down into 12v 100 AH or 6 volt 200AH packages or there abouts.

either two 12 v batteries in paralell or two 6 volt batteries in series

The other thing to consider is the N70 size battery is the most common and bang for bucks battery on the planet, because everything uses them, ya more likley to chisel a deal on an N70 than any other battery .... you will have more choice and a better chance of it being in stock.



4/ DC to DC chargers V direct charging from an alternator.

The notion that you can not or will not fully charge any given battery from an alternator is just rubbish, this is proven untrue in both theory and practice.

To compare the two methods of charging and the erroneous insistences we need to look at detail.

A/ ..... One of the contentions here is what is being considered "Fully Charged" and how is this being measured.

IF you take a battery that has been charged as far as it will on pretty much any given car alternator, then put it on a multi-stage "smart" charger, it probably wont read as fully charged .... WHY .... because the so called "smart" charger is making various assumptions and it's end of charge detection may well be at a higher voltage that the alternators charge voltage.

It must be understood that one of the ways multi-stage chargers ( including DC to DC chargers) stick charge to batteries as fast as they do is using voltages that simply would not be safe on a constant rate charger ..... some will push 16Volts in boost charge mode.

Any argument about state of charge has to discuss how that state of charge is being assessed ...... there are only two valid and accurate ways ..... steady state resting terminal voltage ( after the battery has been rested at least 1 hour preferably 4 hours) and electrolite specific gravity.

B/ ... Some batteries require higher charging voltages or require higher charging voltages when they are in certain conditions.

Many older car alternators where regulated at 13.8 volts, this is not sufficient for some ( but not all) batteries.

but those are not the major concern in many situations.

THE major concern

IF I have a 200AH battery and all my cabling is adequate ....... I have a DC to DC charger that is capable of delivering 20 amps .... that battery is at 50% SOC ... it will, take about 6 to 8 hours driving to " fully charge" that battery given charging losses and charge tapering.
In 2 or 3 hours it will not come close to fully charging that battery.

IF however I have the same battery on adequate cabling, being charged from an alternator capable or 120 amps ...... we will start by kicking in 50 or 60 amps and then drop back to 20 or 30 amps as the SOC increases.

In 2 or 3 hours driving the battery will be in a better state of charge being charged direct from an alternator than via a 20 amp DC to DC charger ..... assuming the battery will tolerate the Charge current and has sufficient charge acceptance.

C/ much of the blame for batteries not getting charge, can be due to inadequate cabling ...... cable size is more often than not underestimated.

D/ THE most common reason for batteries failing to charge and failing prematurely ..... is inaddequate charging time ....... no matter what battery or charging system, you cant hammer a battery all night and expect it to come back to full charge in 2 or 3 hours driving.

5/ OH and remember ALL batteries should be house in a situation where they are well ventilated, and acid leakage is considered an inevitable fact.

cheers

AGM batteries are not that expensive when you look at the extra life span you can get out of them. Also they are not suppose to leak acid if the casing cracks or vent gas like a wet cell which would make them safer all round. Also wait till people have a sale I bought an Amptech from Auto Barn when they had a 25% off sale, I also got one from Giant batteries on sale. I bought a Redarc BC DC charger from a 4WD ebay site and saved a couple of hundred on that. So instead of using wet cells in my canopy I could safely fit 2 AGM's maintenance free and hopefully hassle free for possibly 8 to 12 yrs.