AGM Batteries vs Wet Cell

[Nimble1]

OK..Its not a sailboat but I have been using AGM's in my Nimble Nomad trawler for years. I need the AGM's for the non-gassing advantage because the 2 batteries are installed in the cabin. When I first got the boat it had gel-cells installed with a charger that was set for flooded batteries. I had to be very careful when charging and when they died I switched to AGM's. I just replaced my first set after 6 years!! Now, I don't do a lot of cruising but I love the fact that they hold a charge for so long.
I replaced my old ones with Optima spiral cells from Sam's Club, I paid $155.00 a piece for them and hope that they last as well as the old ones. I have been laid up due to surgery and unable to boat so they have been sitting a while. I checked them last week and they were holding at 12.6 volts after sitting 2 months.

Tom Nowling
Nimble Nomad "Sweet Pea" hull #1

[Hope Light]

I'm about to invest again in batteries and if cost wasn't an issue would be going for flooded Surrettes again. A friend, who is a marine surveyor in Annapolis, an electrical engineer and a cruising sailor with thousands of offshore miles says he sees many experienced cruising sailors going back to flooded batteries after having a less than satisfactory experience with AGMs. It seems many sailors would rather do other things like spearfishing, walking beaches and drinking rum rather than hanging around the boat to make sure everything is charging at just 13.71876 volts so the AGMs wont be damaged. An overstatement to be sure but the fact is that many are happy to not have to worry about exactly what is happening. Flooded seem to be more forgiving and so I will go the golf cart type route I think. Has anyone ever heard of an explosion from gas escaping from batteries during charging?

[Landshark]

Well, that's an interesting perspective about AGMs, but innaccurate any purely anecdotal. That's why I have a shore power charger and engine a charging regulator that are adjustable to 0.1 of a volt. That, along with a good battery monitor (e.g., XBM) makes AGMs virtually maintenance free. So if you'd rather deal with electrolite, specific gravity readings, gassing, clothes with acid holes, rapid unused discharge, and long charging times by all means stay with flooded battery technology.

[hellosailor]

"Has anyone ever heard of an explosion from gas escaping from batteries during charging?" Not in a sailboat, but there are several thousands of injuries every year from incidents where folks jump started cars or trucks with wet lead batteries--supposedly followed by explosions from hydrogen. This from the companies who sell batteries and jump kits, which now often include goggles because of acid getting in too many eyes.

Flooded absolutely are more forgiving in that you can abuse them and then restore the electrolyte. But in this day and age even a 'cheap' charger or charging system should be able to keep AGMs happy. Kinda sounds like you are trying to say you have a POS charging system and you'd rather not update it--which would be the best reason to go back to 'more forgiving' batteries. Still, the acceptance rate on AGM batteries is 25% higher than wet lead, so if you ar recharging them from an alternator or shore charger? You'll waste one extra hour every four hours, using an obsolete charging system with 'forgiving' batteries.

I'd rather update the charging system, and then if you want "cheap high capacity" use that as the justification for wet lead. They definitely are cheaper, but I can't see any other advantage to them. And I'm not sure they are still 'cheaper' once you factor in 25% more fuel for a genset or alternator to recharge them.

Or course Surette and Rolls and the like are commercial/industrial quality batteries, not just deep cycle or traction grade. It would be hard to find comparable AGMs.

[Hope Light]

Since this is a cruising forum I didn't think I needed to mention that my concern about charging batteries had little to do with shore chargers as they aren't much help between NA and Bermuda nor in the Out Islands of the Bahamas. Also I am often far from fuel supplies and docks and have neither the desire nor capability to easily carry a lot of fuel on a 36' sailboat.
So that leaves alternators and alternative sources of power. High output alternators and high tech voltage regulators such as Balmar produces, as example, are neither brain surgery nor expensive. I went to a 100 amp alternator in 1985 when I first spent the winter in the Bahamas and with 8D Surrettes in those days had no issues at all with power. In future, I would like to lower my Volvo main engine diesel use. The engine drive Seafrost refrigeration takes an hour of running per day in hot weather to make ice. I would like to shorten that engine time by using the Seafrost 110 volt compressor as well as, or instead of, the engine driven compressor for both the frig and freezer. Probably will change the 110 compressor to 12 volt.
When I changed my Raytheon radar to Furuno I also changed the location of the scanner from the mainmast to a radar mast mounted on the stern. I wasn't thinking then I would want to also have a wind generator mast but will install an Air Breeze shortly on an additional mast.
Thanks to those who have responded. If there are others out there who are serious cruisers and whose persective isnt just being at a dock I would appreciate your feedback. I am aware of the basic stories of AGMs and not being able to mount flooded batteries upside down but that has never been much of a problem for me anymore than I have had holes in my clothing from battery acid. So far the only real advantage that I can see is that AGMs hold their charge when unattended. Maybe the best thing can do is stick with Surrettes.
Cheers.

[Landshark]

Hope Light

I think you're missing the point that AGMs accept a much higher charging rate than flodded batteries. Hence, less time spent charging. That means acheiving less engine running time you seek. That's a big plus. Of course, you'll need the charging capability to supply that capacity. As far as cruising goes, I've yet to meet the cruiser that spends more time at sea than at a quay, or anchor, somewhere. Perhaps we'd like to believe otherwise, but it just isn't so.

Landshark

[Hope Light]

Thanks for your message. I do get the point about AGMs being able to take a charge faster but also understand they must not be allowed to go too low and must be charged to capacity each time they are charged, or risk serious damage, which for most real cruisers is unrealistic. I agree that most are not on the move but I am talking about being on the hook away from shore power and civilization.

[camaraderie]

Landshark...while you are correct in principle...the governing factor in HL's scenario is a 100amp alternator. If they have a 500ah wet battery bank or larger, they can use the FULL output of the alternator to put a bulk charge in. The same size AGM bank won't charge any quicker with a 100a alternator. Generally it is not a good idea to fit most sailboat diesels with alternators too much bigger than 100-120 amps due to the wear on bearings...so the quick charge functionality of AGM's is lost to boats with big battery banks UNLESS you have a generator driving a big AC charger.

Hope Light...you are incorrect about the care needed for AGM's. Once you have your charging set up properly you can quite comfortably cruise using 50% of capacity and charging to 80-90% of capacity. You DO need to charge to 100% capacity every couple of weeks to a month in order to prevent sufation but this does NOT need to be done each time you recharge. (We just waited till we went to a dock for a day and used our AC charger. ) In my view, if you pay attention to a few simple things...the AGM's are far easier to deal with in a cruising situation than flooded AND more economical over time.
If you have a smaller than 500ah house bank with your alternator...you will save money more quickly and run the engine less with AGM's.

[witzgall]

One of the things I keep reading about when folks are talking about the virtues of AGM batteries, is reduced charging time. This is a good thing when talking about charging from a shore power charger, or from the engine alternator. So with a big alternator, you can have short chrging times.

But when your goal is to not use the engine at all for charging, how does the situation change?

The scenario is this, extended cruising, almost exclusively at anchor. perhaps a 300ah house bank, and a seperate engine battery. LED lights, Efficient refrigeration, some computer time, perhaps a ventillation fan, and that is about it (when at anchor).

Friends are doing this right now with a 200ah house bank, and no refrigeration. They are topped off most days at noon, almost all days by sunset. They are only using solar, 160 watts new panels , +60 watts of old panels. This is cruising in the Carribean.

So my point is that Flodded batteries might make more sense in this scenario? Lower initial cost, less change of gassing since most chargin is done more slowly, and easier to replace in case of failure in a distant port.

BTW, I have thusfar installed one Trojan 1275 Plus wet cell, rated at 150ah. This is the largest 12v battery I could find that fits in a GRP 31 footprint. Two of these +300ah, for less than $400. And they won't take up any more precious storage space on our boat.

Chris

[Hope Light]

Chris, you have crystallized this issue for me in that I have no desire for a huge engine and would like to decrease dependency on my main 37 HP Volvo diesel.
Having to find shore power every few weeks and/or needing to run the engine for long periods, even every few weeks, to top up the AGMs doesn't appeal. It seems everyone who has responded in favour of AGMs has mentioned shore power one way or another. A recurring theme. So bottom line is that shore power has no place for me in cruising whatsoever. It has lots to do with spending time at the dock or in marinas. In that scenario a 60 amp bargain basement battery would do me fine.
To follow your scenario in the Carribean, I will have a 400 amp plus house bank and another 200 plus amp bank that is much more than just a starting bank. In addition a Surrette 31, 108 amp dedicated to anchor windlass. Banks are isolated from one another.
I plan to add solar and wind generation as well. In this day and age it seems stupid not to.
Thanks.

[Hope Light]

Camaradarie, your points are appreciated and make a lot of sense. They help to sort out the pros and cons of it all. Running the engine less is a goal but I also have to consider that I will putting in dribs and drabs of charge with solar and wind which are variable in frequency and quantity. Thanks.
David

[camaraderie]

My pleasure David.For both Witzgall and you... I ran both solar and wind on my last boat (160watts + 4winds gen) and managed pretty well on the average 100ah I got per day from them in the Caribe. had to run the engine with 110Balmar every couple of days for a bit as my usage was high at 150ah/day...fridge took half of that in the tropical conditions. With ONLY solar and wind and constant on board systems running it is rare that you get to 100% charged. If you are NOT going to get to 100% on a semi regular basis...then I absolutely agree with the decision to go with flooded. Note that with flooded you will have the EXACT same situation occur as with the AGMs...sulfation and loss of cycles and amphour capacity. You will need some way to equalize your batteries to 15.5V once a month or so for 8 hours or you will have greatly reduced flooded battery life as well. Fortunately...if you go with wet cells...they CAN be eq'd unlike most AGM's....and if you ruin a bank of cheap flooded batteries...you're only out about 1/3 of the price of AGM's that aren't taken care of!

Chris...just a side note. I think you need a bigger battery bank if you want NO engine running time. Even a small, efficient fridge and the needs you state will result in at least 100ah per day. A 300ah bank give you the ability to use 150ah's. What happens when the sun doesn't shine for a couple of days and the wind stays under 10 knots? You either run the engine or have dead batteries on day 2. I would have at least a 400ah bank for your "no engine" goal.

Anyway...there's a few things to think about. We each have to do it our own way in the final analysis!

[witzgall]

300ah might be enough, or maybe 400 or more is appropriate, we will see. Concerning equalization, Outback's Mppt solar controller has an equalization setting, I am thinking this may do the trick. Off the grid homes have been doing equalization this way for awhile - just wait for a real good solar day, At least during the sunny months.

One unknown for me is venting. The compartment these wet batteries are in is underneath the head of the quarter berth. It is not vented currently. If I only charge hard when the companionway is open, which is right next to the batteries, is this safe? Is there another way to safely vent, so that seawater cannot get into the battery compartment?

Chris

[sluissa]

I think the idea is to just not let the gasses build up in the compartment with the battery. Hydrogen rises. If you have any kind of ventilation, it should be sufficient.

[hellosailor]

Hope-
"...AGMs...must not be allowed to go too low and must be charged to capacity each time they are charged, or risk serious damage, "
Not quite right. AGMs no different from any other lead batteries in that respect. If you drain them too deeply, you reduce their overall life. But you do NOT damage them by failing to fully recharge them. If anything, they'll take less damage than wet cells because the physical mechanism for sulfation is different, and sulfation is less likely to happen. (The precipitates simply cannot fall to the bottom of the case, as they do in a wet cell. The chemicals are trapped in the glass mat, where they are more likely to be reverted back.)
The ONLY disadvantages to AGM are PRICE, and NO OVERCHARGING. Once you overcharge them, you boil off electrolyte that can't be replaced. In a wet cell, it can be replaced.
Further, wet cells must be given an EQUALIZING CHARGE which is a higher-voltage charge, about once a month. Every AGM manufacturer (except Concorde/Lifeline) says DO NOT equalize AGMs. Less routine maintenance to do.

WRT to venting, consider this. Many car enthusiasts have relocated their batteries to the trunk. One of the Fiat sportsters used to have the battery in the trunk from the factory, for balance. And battery acid vapors cause problems and corrosion for all of them. Enough so that Mazda (the Miata has a rear battery) only uses AGM for them, and BMW, who use a wet battery in rear of the X3/X5 series, run a dedicated external vent tube beneath the car.

Charging wet cells gives off corrosive vapors, not just explosive hydrogen gas. They really should be in a dedicated sealed compartment--vented overboard. "Hydrocaps" will help that, they use a catalyst to recapture some of the vapor during charging, also preventing some electrolyte loss.

Don't mistake me for being an "AGM only" guy, the price and availability of wet cells are both strong arguments in their favor. (Pssst! Wanna buy some acid-burned clothing?!)