# Replacing gel battery



## Grunhilda (Jul 9, 2007)

Our gel battery has died after 5 years, we'd like to take the opportunity to add another leisure battery. The handbook says you must replace with another gel battery. Does anyone know why we should? I'm baulking at buy two gels if it's not really necessary.


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## DABurleigh (May 9, 2005)

Some gels have a different charging regime from wets.

I have always thought whereas you should not use a wet charging regime on a gel, using a gel regime on a wet should not be a problem.

Others maintain differently, though don't explain why in terms of battery physics.

I do differentiate between problem and optimum here.

Dave


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## Wizzo (Dec 3, 2007)

One possible reason is that there is no external vent from the battery box? Standard lead acid batteries produce an amount of hydrogen gas when charging which is OK provided the battery has ventilation to the outside but could prove dangerous (explosive) otherwise.

JohnW


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## DABurleigh (May 9, 2005)

Well that's more to do with the sealed aspect rather than gel (many wets have sealed) but I take your point. Unfortunately people are conned by marketing that says unvented sealed batteries are OK in a habitation area, whereas they are not. 

In a failed cell condition, most chargers will generate hydrogen at a rate that any recombinant valve will not cope with, so the seal will vent anyway.

Good quality sealed batteries have a venting arrangement as well, so that in this situation the hydrogen is vented harmlessly to outside.

Dave


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## CliveMott (Mar 10, 2008)

Gel and AGM batteries usually require a higher terminal voltage during the later phases of charge in order to achieve the maximum charge. The problem with fitting a WET electrolyte battery to a charging system optimised for GEL will be excessive gassing and potentially decreased battery life. However most charging systems have the ability to set the output for GEL or WET either by links, switches or software using the dealers laptop. You need to check this aspect out with the motorhome manufacturer.
However motorhomes set up for WET batteries will work with GEL or AGM but the effective capacity will be a tad reduced. I guess that the continuous use of the battery which is never allowed to become fully charged may also lead to a reduction in its service life.

Hope that helps.

C.


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## DABurleigh (May 9, 2005)

Thanks, Grandad  That resolves the experiences of some. I wonder why the higher voltage (than that for wets) is "needed", and why that is more detrimental to wets. Hey ho.

Any views on why manufacturers, converters and dealers get away with installing unvented sealed batteries in the habitation area?

Dave
PS Yesterday first time in the NF since you last spotted us. But had son & g/f with us, and walking to spot where scattered Mum's ashes. Late pub lunch just north of Ringwood then drove home in the dusk. Exercise & fresh air made me sleep like a log.

PPS. Here's one thing you don't know about lead-acid batteries despite a career in working with them. 80% of the voltage is entirely due to Einstein's relativity!


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## spatz1 (May 19, 2011)

CliveMott said:


> Gel and AGM batteries usually require a higher terminal voltage during the later phases of charge in order to achieve the maximum charge. The problem with fitting a WET electrolyte battery to a charging system optimised for GEL will be excessive gassing and potentially decreased battery life. However most charging systems have the ability to set the output for GEL or WET either by links, switches or software using the dealers laptop. You need to check this aspect out with the motorhome manufacturer.
> However motorhomes set up for WET batteries will work with GEL or AGM but the effective capacity will be a tad reduced. I guess that the continuous use of the battery which is never allowed to become fully charged may also lead to a reduction in its service life.
> 
> Hope that helps.
> ...


i think you ll find you got that the wrong way around...

Apparently you can damage a sealed/agm at above 2.35v per cell at which point gassing occurs , but you can charge a wet to 2.6v per cell to equalise..

http://screencast.com/t/xrd6CBBNtzV


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## CliveMott (Mar 10, 2008)

Grandad my a--e!
Seasonal Salutations also to Alison and the brood if you have then there. We have +1 here (96 year old) and await the arrival of another 8 today.

Well, all of these batteries are variations of lead-acid batteries so there is a lot of similarity. I do not know for sure why the voltage is greater for GEL & AGM but I can offer a possibility. Wet electrolyte batteries naturally "stir" the elecyrolyte because of internal heating and also gassing thus assisting the acid to continuously mix and remain equal in strength. The acid will better reach all the lead paste and be part of the active chemical change. Gel or AGM batteries do not stir so a higher voltage is necessary at access those parts of the plates that would be traditionally the last to be changed chemically. Charging systems set for GEL normally have a tight time limit set for the high voltage phase. Thats my guess.

All batteries should vent to outside the vehicle, either by being in an outside locker or by using batteries that have a venting manifold attached to a tube that goes outside. Any that vent inside the vehicle are simply wrong. Some of our smaller converters are very bad at this and I have seen examples of internal venting and also battery cables bent round sharp metal corners on brand new conversions at the NEC frequently. I had best not mention names on this forum though.
It is a detail that potential buyers need to watch

C.


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## DABurleigh (May 9, 2005)

Crikey. Put your feet up for a doze quick. You oldies won't last the day hosting a crowd  Anyway, enjoy the company of your family.

Glad you agree on the venting. On this point on MHF I felt a lone voice in the wilderness. 

Give me wets plus maintenance caps any day, and a Halfords washer tube poked through the floor. Then if I want maintenance free, just switch to a charging regime that doesn't go above 14.4V (though I equalize once a year to get rid of the accumulated lead sulphate crystals). If I want maximum oomph, gas them at 14.8V and check levels a couple of times a year.

Dave


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## DABurleigh (May 9, 2005)

Hmmn. Can't see why sealed should have a higher voltage than wets at any phase, though I can see why the absorption phase may be longer, for the reason you give. And if this is somehow enforced by the charger battery type setting, MAY be a reason why to avoid wets on a gel setting. But I remain to be convinced; I tend not to be unless I understand 

AGM charging regimes sometimes have a higher voltage phase but this is de-sulphation/ equalisation put into each charging cycle because I guess their plates are more affected by sulphation.

Dave


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## Glandwr (Jun 12, 2006)

Notice in my battery locker saying only use Gels. However there is a set of jumpers on the charger electro bloc thingy that allows a change to wet. As dave says different charging regime. Have a look at your charger. Changed ours to wet and had no probs.

Dick


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## Grunhilda (Jul 9, 2007)

Thanks Glandwr, that's exactly what my husband found, a switch by the charger thingy 'Gel' or 'Wet'.


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