Thread: Mixing AGM and wet cells...

Eddie

I'm happy to be proven wrong here, but I don't see the problem with gassing of a wet cell inside the vehicle.

A properly managed wet cell battery (i.e. being charged within its specified limits and not being boiled) doesn't really gas very much at all. The regulator on the alternator circuit stops the battery from boiling.

I have one inside a battery box in the rear of my 110 wagon, and I'm yet to smell it gassing. It gets charge from both the alternator and a solar panel and runs a 55 litre fridge all day every day.

AGMs are hugely expensive when compared to the wet cell batteries. Maybe there's an advantage that I have yet to discover.

Regards
Scott

I don't know that you would get to smell gas from a battery, Hydrogen gas in its pure form is odourless. It could be that some other element is involved but I am no chemist and high school chemistry was a while ago now. Problem with hydrongen gas venting is that it is explosive and in an area where it is not well ventilated it can build up.

From Battery Tutorial | Batterystuff.com


"Wet Cell (flooded), Gel Cell, and Absorbed Glass Mat (AGM) are various versions of the lead acid battery. The wet cell comes in 2 styles; serviceable, and maintenance free. Both are filled with electrolyte and I prefer one that I can add water to and check the specific gravity of the electrolyte with a hydrometer. The Gel Cell and the AGM batteries are specialty batteries that typically cost twice as much as a premium wet cell. However they store very well and do not tend to sulfate or degrade as easily or as easily as wet cell. There is little chance of a hydrogen gas explosion or corrosion when using these batteries; these are the safest lead acid batteries you can use. Gel Cell and some AGM batteries may require a special charging rate. I personally feel that careful consideration should be given to the AGM battery technology for applications such as Marine, RV, Solar, Audio, Power Sports and Stand-By Power just to name a few. If you don't use or operate your equipment daily; this can lead premature battery failure; or depend on top-notch battery performance then spend the extra money. Gel Cell batteries still are being sold but the AGM batteries are replacing them in most applications. There is a little confusion about AGM batteries because different manufactures call them different names; some of the popular ones are sealed regulated valve, dry cell, non spillable, and sealed lead acid batteries. In most cases AGM batteries will give greater life span and greater cycle life than a wet cell battery.
SPECIAL NOTE about Gel Batteries: It is very common for individuals to use the term GEL CELL when referring to sealed, maintenance free batteries, much like one would use Kleenex when referring to facial tissue or "Xerox machine" when referring to a copy machine. Be very careful when specifying a battery charger, many times we are told by customer they are requiring a charger for a Gel Cell battery and in fact the battery is not a Gel Cell."

AGM sprial wound batteries like the yellow tops are tightly packed and resist vibration better that your standard plate battery suspended in electrolite.

Originally Posted by scanfor

Eddie

I'm happy to be proven wrong here, but I don't see the problem with gassing of a wet cell inside the vehicle.

A properly managed wet cell battery (i.e. being charged within its specified limits and not being boiled) doesn't really gas very much at all. The regulator on the alternator circuit stops the battery from boiling.

I have one inside a battery box in the rear of my 110 wagon, and I'm yet to smell it gassing. It gets charge from both the alternator and a solar panel and runs a 55 litre fridge all day every day.

AGMs are hugely expensive when compared to the wet cell batteries. Maybe there's an advantage that I have yet to discover.

Regards
Scott

The problem with a wet cell battery inside the vehicle is not the hydrogen - as you point out, unless there is a regulator failure (and these DO happen), there will be little gassing, although the amount depends on how much hardening metal is alloyed into the plates (most modern batteries have very little).

There are two problems - the first is that the small amount of gas that is given off is carrying an aerosol of sulphuric acid (which is what you smell) which even in very small concentrations is very corrosive. The second problem is that in case of an accident, especially a rollover, the vented battery will spill acid into the interior of the car.

John

Originally Posted by scanfor

I'm happy to be proven wrong here, but I don't see the problem with gassing of a wet cell inside the vehicle.

There is no real reason for not using flooded wet cell batteries inside a vehicle and in fact is still a common practice used in many of the vehicles imported from Europe.

VW vans and Fiat small trucks, used for camper vans and small motor homes come with wet cell cranking batteries located inside the cab, usually under or just behind the seats.

The irony is that the house batteries, which are most likely to be AGMs, are usually mounted in an externally vented battery box elsewhere in the the vehicle.

JDNSW

I agree with you about the spillage in the event of a rollover.

My judgement on the potential for problems caused by the corrosive nature of the gassing is based solely upon the premise that the battery box under the passenger seat is full of relays and electrical contacts and none of these seems to have any corrosion evident after 10 years of being located in the same compartment as the main wet cell starting battery.

I'm not sure how much gas would be emitted by either the start battery or the deep-cycle battery when it is recovering from discharge. It would be interesting to know.


Regards
Scott

Thanks guys - so gassing isn't a huge issue (I assume with how drafty the Defender is anyway, gassing wouldn't be too much of a problem regardless! The entire car's vented to the outside )

But the other issues:

- are AGMs worth the difference, if we ignore the gassing? I've read things about quicker charging and longer life span, greater ability to discharge deeper, etc. which might make it worth the extra money...
- and does mixing an AGM with a wet cell battery when using a smart device like the SC80 work ok?

Cheers

Eddie.

Hi eddiec, first off, contrary to all the myths, there is no problems with mixing battery types.

Next, personally, I think good old fashion Flooded Wet Cell batteries are still the best choice in “MOST” cases.

There are some circumstances where AGMs are the better choice but this comes down more to how you are going to store them when not in use.

If the auxiliary battery is going to be permanently mounted the your vehicle then there is no real advantage to forking out the extra expense for an AGM as a wet cell will be well maintained and as such should last for years.

Originally Posted by drivesafe

Hi eddiec, first off, contrary to all the myths, there is no problems with mixing battery types.

Next, personally, I think good old fashion Flooded Wet Cell batteries are still the best choice in “MOST” cases.

There are some circumstances where AGMs are the better choice but this comes down more to how you are going to store them when not in use.

If the auxiliary battery is going to be permanently mounted the your vehicle then there is no real advantage to forking out the extra expense for an AGM as a wet cell will be well maintained and as such should last for years.

Hi drivesafe, are you able to shed any light on the issues I've been having in this thread?
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