AGM vs Gel cells

[nodee]

Carl,
Too soon to report any results as the boat is winterized and the installation was a post season project. Yes, I am actually charging at 14.7-14.8. I am using a Dolphin 12v 80 amp 4 stage charger from Scandvik Marine that came with the boat and they advised the proper setting for Odyssey batteries, so everything should work well. Since the charge voltage is so high I also had to switch out my 2 cranking batteries (more $$) in order to avoid cooking those LA wet cells, however I saved a couple of dollars there by going with Sears Diehard Platinums, which I understand are Odyssey batteries made for Sears.
A couple of notes from the switch:
The Odysseys are essentially 12"cubes and the posts are located on the diagonals. The LAs I replaced were 4Ds with both posts on the same end. This forced me to replace the cables which pushed me to making new 2ott cables. In order to avoid purchasing an expensive crimp tool Battery Warehouse agreed to make the crimps if I purchased the ends from them. I did have to supply the cable from elsewhere as they did not have 2ott tinned marine cable in stock.
Also, the 12"square dimension did not fit my old battery boxes (4D doubles and a 4D single). I was able to fit 2 Odysseys into one 8D box, however I have been unable to locate a single box that fits the 5th Odyssey. I don't have room to put it into 1/2 of another 8D box, so I will probably have to improvise. I had height issues as well as 4 of the batteries were located under a bunk, while the 5th was outside the bunk under the sole. I will probably be fashioning a custom box lid, as well.
So far, though, I am happy with the installation.

[btrayfors]

AGM batteries indeed have lots of attractive features. One of the most touted, of course, is their ability to receive a very fast charge (providing, of course, that you have charging gear which will crank out a lot of amps).

However, they have one serious disadvantage: cycle life.

Look at the referenced East Penn primer on VRLA batteries. Near the end, you'll find a little chart which responds to the question of how deep a discharge affects cycle life.

There, you'll note that with a 50% discharge level -- which is typical for a cruising boat -- the cycle life of East Penn AGM batteries is 370 cycles!

Whaaaat? That's just a little over one year in constant use, assuming one 50% discharge each day.

Gelled VRLA's do much better in this department.

So do flooded batteries.

So....before making the switch to AGMs, you need to carefully consider HOW the batteries are gonna be used.

You can't have it all :-)

Bill

[CarlF]

Thanks Kirk. Are you sure you don't want to do a little mid-winter cruising to test out those batteries? Nothing like a little below zero degrees windchil!

Dave. I totally agree with you on AGM's. The Odyssey claim (and skepticism is always appropriate) is that their AGM batteries are different.

They claim 400 cycles at 80% discharge. At the boatbuilders show one of their engineers said I was reasonable to assume 800 cycles at 50% discharge. The manufacturer also claims that charge rates can be very high. They show a graph showing charging time with a 3.1c10 charge. If I undertand this correctly this is charging at over 300 amps into a 100 amp hour battery. No cruising boat is going to have this sort of charge capacity for a house bank but it certainly suggests some interesting options. Nigel Calder has put them into his new boat with this in mind.

That's why I wish Kevin would try out some winter cruising.

Carl

[bobfnbw]

I like many of you currently am using golf cart batteries, interstate 220ah and have 8 of them.
I am moving the entire bank to under the salon sole. They are almost 11.5" high and that is pushing the limit for my space.
These odyssey's are only 9.2" high, and would fit much nicer.
But 6 of them would cost twice as much as trojans T145s.
The no spill, and faster acceptance rates are attractive, but I am not sure if the life3span would be as good. But with 200-400 amps of solar and a kiss wind generator, and mostly LED lighting and a (future project) very effecient Fridge and freezer, maybe its a good choice.
I think I have about a year before I have to replace these.
What do you think would be a better overall plan in this situation?
The extra money would hurt but not a deal breaker.

Bob

[btrayfors]

Bob,

If you have a year before you have to make a decision, I'd wait. There are some very interesting new technologies poised to come on line.

One of the most exciting is that by Caterpillar spinoff, Firefly Energy. Home - fireflyenergy.com

They already have a group 31 battery in prototype testing, and expect to go into "full production" of this battery in the first quarter of 2009.

The demand for their microcell Oasis technology is HUGE. They already supply batteries to the military, and reportedly have contracts to provide new models in late 2009. The trucking, electric car, aerospace, RV, and other markets are lusting after the technology, too, so it may be some time before they can ramp up enough production to let ordinary mortals (like cruising sailors) get their hands on these babies.

But, hey, I need a Group 31 starting battery right now, and if I could get hold of one of their Oasis group 31's I jump at the chance :-)

Bill

[Sandero]

Bill,

You mention that 50% discharge would be typical for a day. That seems high to me. Most cruisers have large banks and some form of constant charge, wind or solar and some intermittant high output such as a high output alternator on duty when leaving a mooring (anchorage) or returning. Offshore passage making is a completely different demand it would seem.

But returning to the main point. My house bank is about 500AH and I rarely, if ever have gone down 250 of those amp hours in a day. On another thread, there was a discussion about using a Honda Genset to "make up" an 80 amp hour daily use. For my bank this would be only 15% and I don't normally even do 80 AH in a typical day.

But my batts are cycling at the full to down 10-15% or so when I am aboard. I don't know if this counts as "cycles" or whether working them this way is good or bad. The deal is for me, that since I run the engine an hr a day for refer and hot water I am daily doing some topping up of the house bank. For me to get them to 50% discharge I would have to do a lot of SSB tx, light up like a xmas tree, run the heat and so forth, which I simply don't do.

I am curious as to what other sailors use AH wise in a typical day on the hook.

[btrayfors]

Jef,

Typical daily draw for a 40-footer is about 100-150AH per day @ 12 volts. Obviously, this varies widely by size of vessel, equipment used, daily routines, etc. Some might squeak by with less than 100AH/day -- especially if they don't have electric refrigeration -- and some will exceed 200AH/day.

The biggest energy hogs tend to be refrigeration and laptops (which often draw 6A or more, just like compressors).

You're right, many boats don't routinely draw down their house banks to 50% capacity, and many have auxiliary charging sources onboard -- wind generators, solar panels, generators, etc. -- as well as big alternators. For these boats, calculating "routine cycle depth" is difficult or impossible.

Probably the best way to increase the longevity of your house batteries -- be they flooded or VRLA (gels, AGMs) -- is to:

1. Have a bank large enough so that you'll only need to draw down about 25-35% of capacity each day;

2. Have plenty of onboard charging power and SMART regulators;

3. Fully charge your batteries whenever possible -- not just to the typical 90%, but to near 100% if/when you can;

4. (If flooded), keep water level 3/8 or 1/2" above the plates; use only distilled water; use captive caps (Hydrocaps or WaterMiser caps) to reduce the frequency of watering; be very careful not to introduce contaminants when you water, using ONLY distilled water; and

5. Perform an equalization routine every few months for flooded batteries, and occasionally for AGMs, depending on manufacturer's recommendations.

Batteries require care to reach their longevity potential. Energy monitors can help you understand what's going on. Even a simple voltmeter can help as well, if you know how/when to use it.

Bill

[bobfnbw]

Originally Posted by btrayfors

Bob,

If you have a year before you have to make a decision, I'd wait. There are some very interesting new technologies poised to come on line.

One of the most exciting is that by Caterpillar spinoff, Firefly Energy. Home - fireflyenergy.com


Bill

Thanks Bill. I forgot about the firefly. Read about it last year. Looks very promising.

Wonder what the cost of those compared to agm's will be like ?
2009 is just days away....

Bob

[CarlF]

Bob,

I'm with Bill. Next year looks like it will have a lot of progress for batteries. With lead prices down we also may see some price drops in all batteries. Even today, the Odyssey is a pretty good deal if you buy the Sears branded one when they are having one of their "10% off everything" days.

I've been watching Firefly for over a year. Bill - what if you and I don truckers caps and see if we can score some of the new Oasis batteries? Maybe hang out in truck stops offering a battery swap plus $100 in cash.

Carl

[cal40john]

Originally Posted by defjef

Bill,

You mention that 50% discharge would be typical for a day. That seems high to me. Most cruisers have large banks and some form of constant charge, wind or solar and some intermittant high output such as a high output alternator on duty when leaving a mooring (anchorage) or returning. Offshore passage making is a completely different demand it would seem.

But returning to the main point. My house bank is about 500AH and I rarely, if ever have gone down 250 of those amp hours in a day. On another thread, there was a discussion about using a Honda Genset to "make up" an 80 amp hour daily use. For my bank this would be only 15% and I don't normally even do 80 AH in a typical day.

But my batts are cycling at the full to down 10-15% or so when I am aboard. I don't know if this counts as "cycles" or whether working them this way is good or bad. The deal is for me, that since I run the engine an hr a day for refer and hot water I am daily doing some topping up of the house bank. For me to get them to 50% discharge I would have to do a lot of SSB tx, light up like a xmas tree, run the heat and so forth, which I simply don't do.

I am curious as to what other sailors use AH wise in a typical day on the hook.

If you believe the data below, then it suggests to get the most value from your battery, you should be typically discharging down to around 40-50%. You get more cycles the shallower the discharge, but total amp-hrs out over the life time of the batteries is less. I haven't seen one of these tables for AGM, so I don't know if it applies.

John

The table below is from the bottom of the page from the link shown.

http://www.glacierbay.com/1batcrg.asp

Typical Cycle Life
(100 amp/hr Trojan Deep Cycle Battery)
Depth of discharge Number of cycles Total amp-hrs provided during service life

10% 6,200 62,000
20% 5,200 104,000

30% 4,400 132,000

40% 3,700 148,000
50% 2,900 145,000
60% 2,400 144,000
70% 2,000 140,000
80% 1,700 136,000

[btrayfors]

Carl,

Love it :-))

That might work, especially if we could find some scantily clad beauty to hand out those crisp new Ben Franklin's!

And, of course, to help us carry the new Oasis batteries...I think they're pretty heavy.

Would really love to put one thru it's paces.

Bill

[btrayfors]

John,

I'd take the referenced table with a grain of salt. After all, they're calculating total energy for Trojan flooded batteries and the table shows, e.g., 2,900 cycles for a 50% discharge. That's 8 years of DAILY discharge to 50% and recharge. I'd like to run into the guy who got anywhere near that much life from his Trojans :-)

But, the basic point is probably true if you're considering cumulative energy output over a battery's lifetime.

However, cumulative energy output over time is just ONE of several criteria of which the cruising sailor must take account.

And, of course, in practice it's sometimes very difficult to stick to any prescribed conditions. "Honey", you've GOT to use your hair dryer this morning, because we're only down by 38% battery capacity and I've gotta run the engine soon to leave the anchorage. We really need to get up above 40% usage to be energy efficient!"

Soo.... either she washes her hair again or they stay another day at anchor. Happily, neither is necessarily a bad scenario :-)

Bill

[Sandero]

I suppose with so many 12v refer / frzr systems battery capacity becomes key. I decided to go the route of engine drive and that dropped my AH use way down and forced me to run the engine an hr or so a day to do the refer and as a collateral benefit I charge up the batts and make some hot water.

The down side is that I run the diesel a bit more. For typical cruising we are parked at anchor for several days .. or more at a time and really don't need the engine but for keeping the refer cool. But here we could use ice instead, but we don't because we also like the hot water for showers and dishes.

Fortunately our Volvo has taken this "abuse" pretty well and is still running well after 23 years. I am on my forth set of batts. The OEMs were wet cells 4D I think which were followed by a pair of 8D gels and then a gave the wet cells another try (cheapies which I cured me of that) and went to AGMs which are probably nearing the end of their life a 4 yrs. The use is hard to calculate but include 4 years of live aboard cruising and fairly heavy weekend use with a yearly 2 week plus cruise. So I've gotten on the average about 5-6yrs from a set of batts.

Since I have redone all the electrics, with an echo charge and a solar regulator plus a separate start batt I am hoping that the next set of next generation batts will give me 10ys. But one thing, I will never mess around with wet cells again. Too much trouble and I ruined too many clothes!

[CarlF]

Bill.

If you see a "scantily clad beauty" and think "Gee, she's just what I need to carry a bunch of truck batteries around", you're getting old.

Carl

[vacendak]

btrayfors,

what are the preferences of Fireflies, compared to Odyssey's 2150/31 ?
Fireflies have less cranking CCAs, shorter design life, are not in production yet

May ~5% weight saving be of big importance ?