GEL battery > Why?

**Troubadour** · 21-08-11, 10:27

Originally Posted by greenalien

The biggest problem with gel batteries is not getting power out of them, it's putting it back! They have to be recharged quite slowly and need very careful regulation of the charge voltage. This makes them ideal to keep topped up by solar panels, for example, but not so good with an alternator with just a basic regulator (which you don't have anyhow!). For charging from shore power, an intelligent charger is recommended. Get hold of a copy of the technical specs for the battery and see what the spec has to say about charging.

Agreed, this is one of the reasons I don't like gel for cycling.
You can only recharge slowly because you can't tolerate any significant water loss - you can't replace it - and recombination of gas produced during charge is much less efficient than in an AGM type battery. Initial charge current for a given voltage will also be lower than with AGM because of higher internal resistance, i.e. charging will be slower.

**Troubadour** · 21-08-11, 10:35

Originally Posted by nigelmercier

Battery manufacturers often quote capacity at different discharge rates (5H, 10H etc). I imagine that the figures have got mixed up by their marketing department.

I think it's too big a difference for that. I seriously wonder if an initial "1" has been missed off and not noticed. It would be a plausible number for 20hr rate. Without doing detailed figures I think 650 would be too low even for 1hr rate!

**Troubadour** · 21-08-11, 11:46

Zuzullo

Have a look at http://sonnak.com.loopiadns.com/wp/w...NO_web_new.pdf

What I can read of this brochure suggests to me that for the Dual battery, the Wh capacity they give is a downrated figure to give an acceptable cycle life, not the actual capacity.

They seem to claim a life for the Equipment Gel of 1000 cycles to 50% of nominal Ah capacity (IMO ambitious but possible), but for the Dual (bigger but cheaper), only 300 cycles to 50% of nominal Ah capacity (IMO reasonable). (Small graphs on pages 7 & 8).

All you can do is trust their figures and calculate which one is your optimum solution taking into account your priorities.

If you decide to go for the gel, make very sure that your charging arrangements are good enough.

Your decision now!

**zuzullo** · 27-08-11, 09:10

Ok guys, Thank you all for your input!

After talking to the suppliers there is a chance to order this AGM version and I have the money for it. The only issue is that the guy in the shop keep on insisting that I do not need an AGM on a Boat. But from what I have been reading, + your help, I believe this will be a great solution. The quick-charge seem to be a big benefit for me as on the trip I may stop for an hour somewhere just to buy food and I have the chance for a quick load on it.

I hope I wont regret over the GEL, since there is no price difference.
I leave down here my previews choices so you don't have to get back to the beginning of the Thread:

**Troubadour** · 27-08-11, 18:22

Well, they claim (from the graphs in the brochure):

1000 cycles of 50% i.e. 40Ah for the equipment gel, at continuous low rate discharge

750 cycles of 50% i.e. 50Ah for the dual AGM, or about 850 cycles of 40% i.e. 40Ah discharge to compare with the gel one (measure the graph yourself)

250 cycles of 50% i.e. 71Ah for the dual (wet), or about 400 cycles of 28% i.e. 40Ah discharge to compare with the gel one (measure the graph yourself)

The gel will be the slowest to charge and the easiest to damage (particularly by wrong charging), and it's designed for steady low rate loads whereas you have suggested you sometimes want to use fairly high loads.

The gel one weighs 27kg, the AGM 32kg and the wet one 35kg. The weight is dominated by the lead content and more lead is good!

Personally I'm in no doubt I would go for the AGM over the gel. It's better technology in so many ways, it's got more lead in, it will charge quicker and the price is the same. IF the gel one achieves more cycles it's not because it's gel, it's because of other constructional differences which are consistent with the low rate output specification (heavier separators, thicker plates etc).

There is actually a good chance I would go for the wet one. My industry experience makes me view the life claims for the gel and AGM as probably optimistic, and for the wet one as probably conservative. However my experience is not up to date, and maybe AGMs have genuinely improved. We and our competitors were claiming similar figures years ago, but frankly not achieving them very consistently!

The catalogue weight of the wet one worries me a bit, it should be more in proportion to capacity. It looks odd; the 140Ah AGM weighs 45kg and AGM would normally be a bit lighter than wet. If those weights are confirmed it would push me towards the AGM one. If you're considering the wet one you might want to compare other manufacturers weights, you'll find some catalogues on line.

But it's you choosing, not me! Good luck.

PS Interesting to note that the "dual" wet batteries, comparing the same capacities, weigh the same and have the same cranking capacity as the wet start batteries in the catalogue and mostly - not the one you are looking at - the same dimensions. This suggests they are really just starter batteries probably with dual separators fitted, the sort of thing normally sold as a caravan or leisure battery.
Prices of all the batteries you've shown look very high (compared with UK). Is it because they are DNV approved? Are you required to use an approved marine battery?
Compare http://www.tayna.co.uk/Numax-Leisure...es-S284-1.html for example.

**Yacht Yogi** · 27-08-11, 19:19

I have an aeroplane with an expensive gel battery and I have had one destroyed by cold winter weather. I have a friend who is keen on motorcycles which happen to have gel batteries and he and his pals are always having to replace batteries after the winter frosts (bikes kept in garage). To prevent a gel battery being destroyed by frost you must either take it home an keep it warm and/or get a SPECIAL FOR PURPOSE battery minder trickle charger. Don't use a regular car battery charger because the battery plates are too delicate. My special charger cost £140 but it saves on having to replace the battery if caught out by a sudden spell of frosty weather.

**Troubadour** · 27-08-11, 21:41

Originally Posted by Yacht Yogi

I have an aeroplane with an expensive gel battery and I have had one destroyed by cold winter weather. I have a friend who is keen on motorcycles which happen to have gel batteries and he and his pals are always having to replace batteries after the winter frosts (bikes kept in garage). To prevent a gel battery being destroyed by frost you must either take it home an keep it warm and/or get a SPECIAL FOR PURPOSE battery minder trickle charger. Don't use a regular car battery charger because the battery plates are too delicate. My special charger cost £140 but it saves on having to replace the battery if caught out by a sudden spell of frosty weather.

That's interesting. I don't know any reason why gels should be more frost sensitive unless left discharged. Gels and AGMs are potentially more susceptible to frost damage than flooded if left discharged - which they NEVER should be - because the specific gravity tends to go lower.

I don't actually know of any aircraft starter batteries that are gel although there are quite a few AGM ones now - are you sure it's gel please? What make? In fact gel is not normally used for any high rate application.

I used to use an AGM battery in an aircraft, left it on in the winter and had no frost problems, in fact I've started it well below zero (24Ah battery to start an O-200)

Re gel chargers, it's not the plates that are too delicate. It's the gel that dries out if charged incorrectly i.e. at too high a voltage. Same result - battery kaput!

**Stu Jackson** · 27-08-11, 21:52

Before you spend your money on an AGM battery, consider this information:

http://forums.catalina.sailboatowner...d.php?t=124973

**Troubadour** · 27-08-11, 22:48

Most of the Catalina thread is saying that AGMs are less tolerant of abuse than flooded cells and they don't like being left part discharged. Both true. Also true of gels.
AGMs are the quickest to recharge at normal voltages. Not so much because of the very high initial current, but because up to quite a high state of charge, they will continue taking a charging current higher than wets or gels.
You can equal it with a wet battery by using boost voltages and accepting some water loss. You can't do it with gel at all.
It is true that any battery only charged by a main engine driven alternator is unlikely ever to be fully charged. Not good for any battery.
AGM is certainly not always right but I think that thread is a bit OTT.

**zuzullo** · 13-09-11, 12:11

I am testing an old car wet battery to learn a bit more how it works before I invest in a really good one.

So far I am very surprised:
With a full charge of 12.8v it takes more then 20h to get down to 11.2v.

I had all lights on, laptop charging through a [12-230v, 100W] converter and playing music on the radio with 2 big speakers [200w]. At that point I could still push the music volume with no lack of performance and the lights didn't blink at all. I didn't push the battery further as I learned here that we should not empty it completely

So this is my reference on a 64Amp. wet battery. Not bad. But I remain curious to know when it would affect the performance of the equipment.