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Old 30-12-2015, 05:28   #1
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Batterie Gel or AGM

Not too clued up on batteries, but my engine starting batteries are now 5.5 years old and whilst they are OK I feel it would be prudent to fit new ones. When I ordered my Lagoon 400 I ticked the box for GEL they have been and still are fine except the Genset starter battery I replaced after four years. I think I will stay with GEL batteries as I assume the charging system being alternators, solar, and generator are set up for GEL. Any one have any preferences.
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Old 30-12-2015, 05:46   #2
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Re: Batterie Gel or AGM

Typically, the start battery sees very little cycling and lasts a very long time. Ours are just cheap automotive batteries and they started to go bad at year 14.

I wouldn't worry about yours unless they are exhibiting signs of failure. Then I would just replace them with cheap automotive ones - your 14.2V gel charging will be just fine with those in this application.

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Old 30-12-2015, 05:51   #3
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Re: Batterie Gel or AGM

Well, I am far from being a battery expert, but my boat was factory equipped with AGMs for starting batteries - same as the house batts - which I never understood. My understanding is that you don't need deep cycle batts for starting batts. Cold cranking amps is the metric, I've read. So when I replaced mine when the first one died I chose simple, economic, garden variety marine starting batts. I don't see the need for anything sexier.

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Old 30-12-2015, 08:26   #4
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Re: Batterie Gel or AGM

For a cat there isn't much to gain with AMG or Gel. Standard batteries hold up just fine.

AMG and Gel are handy if the batteries won't be level or get sever abuse. If your cat is heeled enough to be a concern, you have other issues than batteries.
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Old 30-12-2015, 08:38   #5
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Re: Batterie Gel or AGM

There is also the issue of some cats having their battery storage in difficult to access spaces. This would make gel/agm advantageous.

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Old 30-12-2015, 10:51   #6
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Re: Batterie Gel or AGM

One reason to consider AGM starting batteries is for consistency if you have an AGM house battery bank.
It's best not to mix systems that have different charge acceptance and float rates.



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Old 30-12-2015, 11:56   #7
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Re: Batterie Gel or AGM

FLA batteries will exist just fine with an AGM charge routine - there really isn't any difference between the two. Gels require lower voltages during charging, but even this won't matter at all for the type of use a start battery gets.

Consider that a typical flooded automotive battery is continually charged by a constant 14-14.2V, and they last just fine for many years.

A boat start battery sees much lower use than a car battery.

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Old 30-12-2015, 12:12   #8
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Re: Batterie Gel or AGM

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Originally Posted by peterp View Post
Not too clued up on batteries, but my engine starting batteries are now 5.5 years old and whilst they are OK I feel it would be prudent to fit new ones. When I ordered my Lagoon 400 I ticked the box for GEL they have been and still are fine except the Genset starter battery I replaced after four years. I think I will stay with GEL batteries as I assume the charging system being alternators, solar, and generator are set up for GEL. Any one have any preferences.
We have lead acid for both starting and house batteries. Our 6 x Trojan T105s are 8 years old and still working well although they do consume lots of water now they are near end of life.

I have substantial experience with vrla and agm batteries used in mission critical systems. Little benefit over lead acid for our needs. They are liked by those organizations who want to minimize osha exposure risk but they have little to no performance benefit over lead acid.

The lithium based batteries offer next generation performance but require good management as they dont like to be over charged.

We'll replace our trojans with trojans. The assumption being we wont see next gen batteries for at least 5 years.

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Old 30-12-2015, 12:36   #9
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Re: Batterie Gel or AGM

Before this thread goes off in an esoteric or pedantic direction, it is important to keep in mind the OP is only asking about start batteries. They will only be put in use for a few seconds once or twice a day at most (probably much less), after which they will be recharged every time.

In this application, a cheap Wal-Mart automotive battery will last many years. Even with a suboptimal charge regime.

However, if the OP's current start batteries are gel, they probably have many more years left in them and don't need replacing at all.

My recommendation is to have them tested before swapping them out - particularly before spending a lot of money on gel or atm.

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Old 30-12-2015, 13:20   #10
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Re: Batterie Gel or AGM

Good advice, Mark. My original AGM starting batts lasted 11 years - a couple years longer than the identical house batts. I just waited for one to die, knowing I can cross connect the house batts to start the engines. When that happened I replaced both of them with generic starting batts.

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Old 30-12-2015, 14:58   #11
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Re: Batterie Gel or AGM

I'm with Mark here.
Start batteries should not be "deep cycle" and have generous CCA to exceed the engine manufacturer's recommendation. In my view, on a stable platform like a mid size cat, mounted aft, they don't need to be "marine" grade. FLA's are fine in this context. They are the cheapest in the $/CCA/service life analysis, but do need some ventilation and periodic (monthly) inspection of fluid level especially if they sit on a charger at the dock. "Low maintenance" batteries will still need periodic checks as well but offer increased opportunity for inspection apathy. Short battery cable length is optimal.

In some "factory" setups, one or other of the engine batteries will be used by the anchor windlass and in my case, the power winch too, so they do see some loads beyond just starting the engines.

Nevertheless, they should sit on a completely separate charge circuit/channel to the house batteries at both the engine alternator connection (think diode based or FET based battery isolator) and at the 120-240V battery charger or Solar charge controller connection.
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Old 30-12-2015, 15:22   #12
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Re: Batterie Gel or AGM

Peter, if you chose Gel batteries as a Lagoon factory option then all batteries supplied are gel. House bank as well as start. This allows charging voltages to be consistent within the boat.

In my boat the factory supplied start batteries are both huge 110 AH Mastervolt gels; total overkill, as is the 70 square mm battery cable. No wonder Lagoons aren't light!

These gel start batteries should last 8 to 10 years, I am told. If they show signs of deterioration then no big deal. Just use the standard Lagoon linkage switch to join both to boost the sluggish battery. I'd be spending money on more necessary boat jobs; I'm sure there are some. Happy New Year!
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Old 30-12-2015, 15:47   #13
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Re: Batterie Gel or AGM

Over spec cables are not to be sneered at especially when cable run is long, for example when traversing between hulls for the port to starboard battery link.

When a current of 100 A flows through a cable of 50 mm> cross section (AWG 0) and 10 m length (30 ft), the voltage drop over the cable will be 0,26 Volt. Similarly a current of 50 A through a cable of 10 mm> cross section (AWG 7) and 5 m length (15 ft) will result in a voltage drop of 0,35 Volt!
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Old 30-12-2015, 16:54   #14
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Re: Batterie Gel or AGM

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The lithium based batteries offer next generation performance but require good management as they dont like to be over charged.
No battery likes to be overcharged. Assuming we're talking about a nominal 12V system, just ensure that the charging voltage for a LiFePO4 battery never exceeds 13.5V and no other management is necessary. That will keep them at about 80-90% SoC. They'll probably last for decades.

The advantages of LiFePO4 are weight, safety, reliability, and long life. The disadvantages are initial cost and the need to ensure that the charging voltage is well-regulated.

Personally, I would never again install AGM, Gel, or any other lead-acid type battery for any purpose.
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Old 30-12-2015, 17:14   #15
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Re: Batterie Gel or AGM

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There is also the issue of some cats having their battery storage in difficult to access spaces. This would make gel/agm advantageous.

Mark
I think that is the key point.

My 24v start batteries are in engine room , well ventilated and can be easily serviced, so happy to stay with cheaper automotive type 8d truck batteries.

However my 24v House are double stacked under dinning room floor, so those are AGM type 8d's
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