GEL battery > Why?

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zuzullo

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These are the only 2 batteries available at my town:

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Why would I go for a GEL battery considering that both claim a 20h constant power deliver?
Here is my purpose:

- Powering: laptop, music (a lot), coffee machine, lights (LEDs), electronics, etc.
- Its a sailboat with no engine. Small outboard (Petrol) only for docking purposes. (can only charge batteries at the marina)
- I live in the arctic with temperatures around -5°C (23°F) for 5month/year
- Sometimes the battery has to remain discharged for 1 of 2 days until I get back to shore.
 
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The benefit of gel batteries is that they won't leak if tipped up. If that is not important to you, get standard lead-acid.

Is your coffee machine heated electrically? If so, it must draw a lot of current. I wouldn't expect an outboard-powered boat to be able to support that.

Pete
 
My understanding is that gel batteries, although being able to cope with deeper discharges than other types, are not good performers at low temperatures.
So given this choice I would opt for the other one, which seems to be a wet battery of the low gassing kind.
You should not let any battery become fully discharged as that will shorten its lifespan significantly. But you could safely take out 70 - 80 Ah from the wet cell battery before recharging and perhaps 55 Ah from the gel battery.
 
prv said:
The benefit of gel batteries is that they won't leak if tipped up. If that is not important to you, get standard lead-acid.

Is your coffee machine heated electrically? If so, it must draw a lot of current. I wouldn't expect an outboard-powered boat to be able to support that.

Pete
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Thanks for your replay.

Well its actually a water boiler. Its a car gadget with a 12v plug and about 20Ah I think :)

Do you think that the movement of a non-gel battery on big waves will affect its power delivery? Of course I will keep the liquid always at it maximum to avoid the lack of contact with the lead.
 
BabaYaga said:
1 - My understanding is that gel batteries, although being able to cope with deeper discharges than other types, are not good performers at low temperatures.

2 - But you could safely take out 70 - 80 Ah from the wet cell battery before recharging and perhaps 55 Ah from the gel battery.
Click to expand...

1 - By "deeper discharges", you mean that one charge will last longer on a gel battery than on other types?

2 - Are those figures related to the batteries power that I have indicated?
Roughly:
I can take up to 55Ah out of an 80Ah GEL battery.
I can take up to 80Ah out of a 142Ah wet cell battery.

Is this correct? Rough figures of course :) Just to have an idea. As this really seem to be important for the choice.

Thanks
 
nigelmercier said:
[pendanticMode]
Assuming this takes, what, 5 minutes to boil a cup. That means it draws 60/5 x 20 = 240A. I think you mean 20A, not 20Ah.
[/pedanticMode]

From the graphs above; the wet battery is a starter, not a deep-cycle. Go for the gel.
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Yes, maybe about 5min to boil.

They also have a dedicated "starter" battery. You can see the charts here: LINK

For me the main question is: which one lasts longer?
WHat confuses me is that they claim that all the batteries last 20h delivering the power indicated. Thats why I dont understand why would somebody go for a gel battery. Maybe because of cold air temperatures and the fact that a sail boat moves a lot on waves and that may affect the performance of the battery!?! Maybe?!?
 
zuzullo said:
WHat confuses me is that they claim that all the batteries last 20h delivering the power indicated.
Click to expand...

The 20 hours isn't a measure of capacity. The total amount of energy you get out of a battery depends how quickly you call for it - if you use it quickly to spin a big motor (for example) then you get fewer amp-hours than if you drain it slowly with some lights. The 20 hour discharge is a standard to ensure that manufacturers are comparing like with like when they publish their capacities.

Pete
 
prv said:
The 20 hours isn't a measure of capacity. The total amount of energy you get out of a battery depends how quickly you call for it - if you use it quickly to spin a big motor (for example) then you get fewer amp-hours than if you drain it slowly with some lights. The 20 hour discharge is a standard to ensure that manufacturers are comparing like with like when they publish their capacities.

Pete
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Ok, so how many Wh are used during that 20h measurement standard?
Isnt that what they right on the box?

650W for the Wet battery
900W for the Gel battery

Can they deliver that for a period of 20hours? Maybe I am totally wrong here :) Sorry, real beginner here!
 
The Ah rating is the number of ampere hours it will deliver in 20 hour to a constant current load. In the case of the gel battery, (85/20)=4.25A load. In practise you don't get constant current loads! A resistive load (lamp or heater) will take less current as the discharge goes on because the voltage is declining. A motor or inverter will take more current as the discharge goes on because it needs to keep a constant power level, so as the voltage drops the current must rise.

The Wh rating is the number of watt hours it will deliver in 20 hours to a constant power load. Initially you would think a 12V 85Ah battery would be (12*85)=1020Wh but it's not that simple because of the declining voltage and increasing current. A constant power load is more demanding than constant current. In this case the rating given is 900Wh meaning it would give 45W for 20 hours.

Note that if you flatten it over 5 hours instead of 20 you won't get 4 times the current or power, you'll get less than that.

In the case of the other battery, the difference between 142Ah and only 650Wh doesn't make sense to me, it's too big a difference. Are you sure it shouldn't be 1650Wh? I would actually expect a flooded battery to have a better constant power performance than a gel battery (because there is less end of discharge acid starvation).

You get a lot more bang for your buck with the wet battery but it MIGHT give you a shorter life. Bear in mind that gel batteries need a much more careful charge regime and are more easily damaged.

Personally I would not use gel for anything. If I wanted a sealed non-liquid battery I would go for AGM every time.
 
nigelmercier said:
Absolutely, but I don't think this is an option in this case.
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Exide Norway does list AGM batteries (but their literature is not clear about the distinction) but yes I noted the OP said he only has a choice of those two.
In that case it would need a very special reason to persuade me to the gel one especially at those prices.
The Sonnak is also an Exide brand so quality should be OK.
 
FANTASTIC. Thank you very much. Now I can calculate my needs :)

The WET battery offers then a 7A, 33W for about 20h. They should write it like so...

Troubadour said:
Note that if you flatten it over 5 hours instead of 20 you won't get 4 times the current or power, you'll get less than that.
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1 - But I get 2 times for sure, right? Maybe 3x?! Thats enough!

Troubadour said:
In the case of the other battery, the difference between 142Ah and only 650Wh doesn't make sense to me, it's too big a difference. Are you sure it shouldn't be 1650Wh? I would actually expect a flooded battery to have a better constant power performance than a gel battery (because there is less end of discharge acid starvation).
Click to expand...

2 - Yes. It seem to be the type of battery. I double checked it on the web site and I was at the shop and its really like that. But the same 140Ah battery built on a AGM technology delivers 1200Wh. This seem to match better your thoughts. :) I need to check the price of an AGM but I dont think they have that!

Troubadour said:
You get a lot more bang for your buck with the wet battery but it MIGHT give you a shorter life. Bear in mind that gel batteries need a much more careful charge regime and are more easily damaged.
Click to expand...

3- Also the rule number 1 seem to be: Never discharge a battery completely. So we cannot count on 20h but maybe 15h? (+-75% discharge). Whats your opinion on this? Maybe this is the plus for the GEL technology. As many say: it is not as bad to discharge deeply a GEL battery than a WET one.
This can be relevant, depending on how much can you discharge each type. (can't find this info)
 
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The two batteries are designed for different use cycles.

The Gel one happens to be a "leisure" battery for supplying lights etc in a caravan, hut or boat with limited charging capability & then being recharged. The wet design is intended for something like automotive use or starting a generator, where there is a VERY high discharge to turn the engine over & start it, followed by a pretty rapid recharge.

This is shown by the discharge curves, the gel one is steady & consistent at a reasonable level, the wet one is able to tae a very high, short term discharge, but then needs a recovery period before taking another (but smaller hit).
 
Searush

Have a look at http://sonnak.com.loopiadns.com/produkter/marine/sonnak-dual (Google does an adequate translation).

The Sonnak Dual is not a pure starter battery, it is a dual purpose type (as one might have guessed!).

I stand by what I said. I still can't understand the very low Wh rating for the wet battery, unless it's possibly a recommended maximum for cyclic use rather than an actual capacity. I suspect marketing as well as technical factors are involved.

http://sonnak.com.loopiadns.com/wp/wp-content/uploads/2010/12/Wh_och_MCA_NO.pdf might explain it but I can't read it!

Personally, for a severe cyclic load I would go for wet first, AGM second and gel a long way third. (That's assuming in all cases that the construction i.e. plates and separators are appropriate, that's more important.)

I could be biased because the company I worked for made wet batteries and was a pioneer of AGM batteries but never made gel. However I think gel is on the way out. It's easier and cheaper to make than AGM but just not as good!
 
zuzullo said:
FANTASTIC. Thank you very much. Now I can calculate my needs :)

The WET battery offers then a 7A, 33W for about 20h. They should write it like so...

*** On their figures yes but I can't understand the low Wh rating unless http://sonnak.com.loopiadns.com/wp/wp-content/uploads/2010/12/Wh_och_MCA_NO.pdf explains it. See also my comments on Searush's post.

1 - But I get 2 times for sure, right? Maybe 3x?! Thats enough!

*** They should have discharge curves somewhere in the literature from which you can work that out but typically yes.

2 - Yes. It seem to be the type of battery. I double checked it on the web site and I was at the shop and its really like that. But the same 140Ah battery built on a AGM technology delivers 1200Wh. This seem to match better your thoughts. :) I need to check the price of an AGM but I dont think they have that!

*** I can only repeat, doesn't make sense to me with present information.

3- Also the rule number 1 seem to be: Never discharge a battery completely. So we cannot count on 20h but maybe 15h? (+-75% discharge). Whats your opinion on this? Maybe this is the plus for the GEL technology. As many say: it is not as bad to discharge deeply a GEL battery than a WET one.
This can be relevant, depending on how much can you discharge each type. (can't find this info)

*** Rule of thumb 50% of nominal Ah. A gel battery is not inherently better than a wet one, in fact i would say not as good. Other aspects of construction are more important.
Click to expand...
..
 
Your 'coffee maker' is over ambitious for your power availability I think. At least with battery life in mind.

To optimise the life of any lead acid battery you need to keep the level of discharge above 50%. Running one 'flat' below about 10.5v repeatedly will kill it very quickly.

I think those coffee makers are 200watts or so. That will need at least 16 Amps. to get a cup of water from ambient to around 60 deg - 5 mins sounds about right, so about 1.5 Ah every cup of coffee.

A car radio ( music ) draws a surprising amount. They aren't designed with power efficiency in mind. With the music going expect 2 to 5 amps. A big drain. 3 or 4 hours of that and you have swallowed 20% to 30% of the battery

LED lighting and yacht electronics ( sailing instruments perhaps a GPS but forget a chart plotter ) are all pretty frugal.

The most efficient way to use a laptop ( another big power draw ) is to charge it before going aboard, use it until it flashes up the low battery warning and then plug in the power adaptor, when it's full disconnect again.

Is a small cheap generator not an option? You could top off the battery once or twice a day and use a small say 500w mains travel kettle to boil water instead.
 
zuzullo said:
1 - By "deeper discharges", you mean that one charge will last longer on a gel battery than on other types?

2 - Are those figures related to the batteries power that I have indicated?
Roughly:
I can take up to 55Ah out of an 80Ah GEL battery.
I can take up to 80Ah out of a 142Ah wet cell battery.

Is this correct? Rough figures of course :) Just to have an idea. As this really seem to be important for the choice.
Click to expand...

1 Yes but only if the batteries compared have the same Ah capacity (which they have not in your case). My understanding is that the rule of a around 50 percent "safe" discharge level for wet batteries can be extended to 70 or 75 percent for gel batteries.

2 They are, but perhaps 70 Ah is a batter figure for the wet cell battery. Remember also that the total Ah capacity will be reduced over time for any battery.
 
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.
 
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