tatra805 wrote:

Ok, well, cant keep out of it anymore

Some battery ranting

Most terms are used mixed and regardless of real construction parameters.
AGM, GEL, Deep Cycle, capacity, etc etc

AGM - GEL –WET
Status of the electrolyte

AGM: inside a glassfibre matting,
GEL: Gel status, not liquid
WET: just the liquid electrolyte


Wet has the disadvantage it will leak when upside down as the electrolyte is a pure liquid. The “plates” are nothing more than lead plates. In the mean time no leaking till 90° for short time solved by matrixes in the battery caps and the plates evolved to matrixed plates for bigger contact surface etc etc

Gel solved the leaking issues, still venting is necessary but the gell is not passing through the sintered filter openings. (eg optima) The disadvantage of gel is that it does not transfer charges as easily,(the gelling part of the formulation is not conducting) hence the need for spiral designs, which just means there is a bigger contact surface between the plates and the electrolyte. This resulted also in a better CCA, as this is directly related.(bigger surface can conduct more energy at same time) But as less active electrolyte per cubic the capacity of the same external volume of the battery is lower. (simply put there is more lead vs electrolyte in it, less electrolyte = less capacity + less electrolyte as the gelling agents are also taking part of the place)

AGM is the “new hot topic” but nothing more than an in-between. Instead of making gell you absorb the normal liquid in a matting. Less chance on leaking + clever venting matrix designs makes them quasi as safe as a gel type. Liquid instead of gel makes for better contact and charge exchange so capacity is up (a bit) and in case combined with a spiral design of the lead plates an even higher CCA than GEL.


(exclude variants)
(note that leaking is also related to gassing when charging, sealed batteries need a better controlled and at lower amp charging process as gasses cannot escape and would make the batteries explode under pressure build up. Also Optima has venting holes, AGM batteries also to allow for a faster charging spec (but still slower than an open battery))

Due to the bigger contact areas (and with the right charging systems) you can “deep cycle” the AGM and Gel better than a simple plate design.
Sulfurisation of the plates is also less an issue as you have more plate surface available. (sulfur on plates= no more conducting, 5% of a classic plate or 5% of a 10 times bigger spiral surface makes the plate is quicker to not charging anymore while the spiral will. It is the charging process that kind of auto-cleans the plates but you need a min current for that which the plates are not able to conduct anymore in that case)

But still, even on optima and others, this is a far cry from real traction batteries which are real deep cycle.

Deep cycling means discharging till 40% of charge. ALL batteries can do this but not all can recover from it. A real traction battery can take up to 3000 deep cycles, a GEL/AGM/ WET deep cycle or leisure battery up to 300, a normal classic lead acid 0 if lucky you’ll survive a couple.

So,if you want top level deep cycling, as you know you will run your batteries empty each and every time and you will only have the chance to charge them x time after that, go for sealed traction batteries. They will cost you 6 times more but you can expect 20 years from them in those conditions. (well, yes 10 years if you flatten them completely 300 times per year… and that is manufacturer guarantee)
You’ll need to build up your banks with individual 6 or 12V cells till you reach your desired capacity.


Now why all this explanation?

There is no reason to prefer GEL or AGM IF you do not have a leaking/positioning issue.

With a wet deep cycle battery you will get:
- normal CCA
- almost double capacity Ah (90 vs 55)
- 1/3 rd of cost
- identical deep cycle resistance

So people into competition that must run under any angle I completely support in their choice of AGM/GEL.

But for campers, overlanding or home warriors I do see a disadvantage in them and although I consider them though and good batteries a waste of money in those situations.

A 50Ah Gel battery will not run your fridge and webasto for 12 hours, even if after recovery the battery has enough juice to restart the systems and run for another hour the build in voltage detectors of your fridge and webasto will switch off after about 6-8 hours.

(not taking in consideration extreme temps/other users which makes things only worse)

With a wet cell you will run them 10-12 hours as you simply have 45% more Ah available.

It was a positive surprise to me to see that Landrover itself selected a deepcycle battery as oem and not a classic car starter battery. (see my previous post)


Another point which I consider important for me.
When putting 2 OEM (or varta’s) of equal type parallel as normal and AUX battery you don’t need a special charging system. When putting a wet and eg an optima in parallel you will never charge them correctly and this will lead to premature failure of the weakest of the two.
So you’ll need to put in a split charging device. (that is not a 100£ fancy battery separator as the national-luna etc, it is a separate charging system as found in marine applications or eg the CTEK one)
Or you’ll have to put in 2 optimas at once. Project cost immediately double and you’ll only have 2x50Ah instead of 2x90Ah. (both CCA enough for starting but the optimas will give in earlier, I guarantee, it's math)

I like equipment and the more the better but not if it is unnecessary.

To me all these batteries have their place and application. But I had too many friends asking me to help them out with constant empty optima’s blaming everything but not understanding that Ah was the only thing they needed in the first place and not the latest hype.

To make it a bit constructive and to answer the original question

1. Don’t deep cycle your batteries, it is an option only for extreme/emergency situations with anything but real traction batteries anyway.
2. Calculate you capacity needed, without that you’ll run out of juice with any type of battery
3. Consider your existing equipment, doesn’t make sense to make things worse.
4. Tune your equipment, right battery for right charging system etc
5. Count your coins as everything is possible and each approach has its pricetag

Respect above 5 and you’ll be a happy camper. Take a shortcut and you’ll put a weak link in the your system.

Friendly 2cents only

PS: I have hands on experience with all types mentioned above except AGM’s. (But also studied their specs) in all different types of applications (stationary and mobile)

Jim G wrote:

Do not use a 'leisure ' battery to start a vehicle, they are different from a standard car battery, they have more or thinner plates, and are designed for slow discharge to a lower level, if you start a car with one then you will buckle the plates and destroy the battery .
There are special ' dual' usage batteries which can be used to start a car in an emergency and are still 'leisure ' type.