Time to replace the house batteries. Has anybody had experience with AGM batteries? I’ve got four 6v flooded batteries for house and an AGM starter battery that seems OK.
I like that they won’t need to be monitored for water, but I’m concerned about capacity.
Thanks for the input.
Craig Stanley
S/V Matou, NS354 #70
Tampa, FL
Charging voltages for AGM and wet cells are different. Not dramatically so but it is a good idea to use all the same type of battery vs mixing them. AGM’s charge faster than wet cells (ie accept more current) so it is wise to check the size of the cables to ensure they are adequate to the task. Particularly the alternator circuit.
After replacing acid-eaten plywood under my batteries (was in there to replace an aged AGM), I would never use flooded batteries on a boat again!
If you go to Batteries Plus you can get the same AGMs (Made by East Penn/ DEKKA) that West Marine sells for $100 less each (200 vs 300?),
I don’t see them on their website, but they had them in-store, and they gave me the 10% web discount regardless.
Thor’s point is particularly important if you have any set-up for charging/maintaining batteries from shore power. The charging systems all need to be set to match the battery type.
I’ve never been able to afford the higher price of AGM, and hence have no experience to offer. From what I’ve read, they do seem to be better. I’ve had very good luck over the years with sealed batteries, which don’t require water level monitoring.
– Bob
Solar Wind
Nonsuch 26C, #143
Building a good battery box is surprisingly simple if you have a table saw. Or alternatively take the measurements to Home Depot and have them cut it..
Measure the battery sides and top to determine how much plywood is needed, allow 1/2 extra
Buy some 3/4" exterior grade plywood and cover one side with epoxy and glass matt.
Then cut out the box , screw together. The inside measurements should be 1 inch larger than the battery including the posts
Make up some thickened epoxy and filet the 8 inside corners.
Drill holes for the cables
I embedded some 1/4" threaded rod in the top ends. Add an additional 4 inch wide strip of plywood across the lid and use wing nuts and fender washers to secure the top.
To keep the battery secure I have old carpet pieces I use on the sides and bottom. The box is secured to the battery platform / hull frame and even upside down the battery will not move.
Just wondering how you tested the upside-down stability, Thor!
Bill Baxter
Persistence NS 30 #507
Penetang, ON
I decided to test the whole assembly for durability so I had a small nip of Glenlivet as a precautionary medicinal measure and stood on my head… , nothing happened to the box so I declared the experiment a success..
On Tuesday, November 20, 2018 at 10:20:08 AM UTC-8, Bill Baxter, Persistence, NS30 #507, Kingston ON wrote:
Craig,
I installed two Lifeline group 31 AGM batteries in La Reina in March of 2005 (that is not a typo, the batteries are over 13 years old) and they seem to basically have full capacity. I have not done a capacity test so can’t say for sure. For the first 5-7 years of their life they did not work hard. Then I added refrigeration and a separate starter battery. Since then the house batteries have worked harder. I try not to discharge them below 50% and to bring them back up to full charge as soon as possible. According to Nigel Calder you will shorten the life of both AGM and wet cell batteries significantly is you discharge below 50%. Don Casey says 40% is the sweet spot. Leaving the batteries in a partial state of discharge for a long period will also reduce the capacity of the batteries. Practical Sailor did a test on this and the results in the May 2015 issue. The results were dramatic. The new Firefly batteries which use carbon did much better in recovering from a partial state of discharge and they can be discharged down to 20% of capacity and still have 1000 charging cycles.
I agree with Thor that you should make sure all of the batteries are of the same type and all of the batteries in one bank are of the same type and age.
Wet cell batteries will give good service if you take care of them and can be cost effective. AGMs are safer and can lay on their side without spilling acid. Generally AGMs are more robust then flooded wet cells but a good quality wet cell is probably just as robust as a good AGM. Good quality deep discharge wet cells such as Rolls and Surrette will have a large number of charging cycles however they take much longer to recharge to full capacity then AGMs and they can’t release current as fast. Good quality AGMs will work better powering a windlass.
I don’t understand your concern about capacity with AGMs. Most 6v flooded batteries are based on the golf cart battery design with regards to size and capacity. Trojan makes golf cart sized 6v batteries in both wet cell and AGM design. They have essentially the same foot print, weight and amp hr capacity. The Lifeline 6v is rated at 220 amp hrs and has the same foot print but is slightly shorter. I have attached the specs for each.
T-105 Deep-Cycle Flooded
|
Capacity Minutes |
Capacity Amp-Hours |
Energy (kWh) |
Dimensions inches (mm) |
Weight lbs. (kg) |
|
@25 Amps |
5-Hr Rate 185 |
1.50 |
Length |
62 (28) |
Reliant T105-AGM Deep-Cycle Reliant™ AGM
|
Capacity Minutes |
Capacity Amp-Hours |
Energy (kWh) |
Dimensions inches (mm) |
Weight lbs. (kg) |
|
@25 Amps |
5-Hr Rate 171 |
1.38 |
Length |
68 (31) |
|
VOLTS |
6 |
|---|---|
|
LENGTH IN (MM) |
10.28 (261.1) |
|
WIDTH IN (MM) |
7.06 (179.3) |
|
HEIGHT IN (MM) |
9.92 (251.8) |
|
WEIGHT LB (KG) |
66 (30) |
|
COLD CRANKING AMPS |
|
|
68F |
1095 |
|
32F |
925 |
|
0F |
750 |
|
RATED CAP. AMPS HOURS @ 20HR RATE |
220 |
|
MINUTES OF DISCHARGE |
|
|
25 AMPS |
492 |
|
15 AMPS |
856 |
|
8 AMPS |
1692 |
Unless you are hooked to shore power or have big solar panels it is difficult to bring wet cell or AGM batteries to a full state of charge. Nigel Calder estimates that realistically when cruising you will cycle the batteries between 50% and 80% of capacity which means you have about 30% usable capacity. With AGM batteries you will get about 1000 charge cycles if you don’t discharge below 50% and you do not leave them in a partial state of charge. With 6v batteries you have to hook two in series to get 12v so four 6v 225 amp batteries will give you 450 amp hrs at 12v (225 x 4 = 900/2 = 450). The usable capacity becomes 135 amp hrs (450 x .3 = 135). With 4 Lifeline 6v AGMs you would have 132 usable amp hrs. The difference is not that significant. The Firefly batteries are rated at 1000 cycles with a depth of discharge of 80%. This means the useable capacity would be 60%. Firefly currently only makes 4v and 12v batteries. The group 31 12v is rated at 110 amp hrs. Two would give 132 useable amp hrs (110 x 2 = 220 x .6 = 132) (I get about 63 amp hrs from my group 31 105 amp hr Lifeline AGMs). If you could squeeze three Firefly batteries into the space you would end up with 198 useable amp hrs.
You have to be careful with the Firefly batteries. They call their 12v a group 31 but it is 13.5" long whereas standard group 31s are 13" long. In some battery compartments the extra 1/2’ makes a difference. For example the extra 1/2" - 3/4" height of the golf cart batteries means they will not fit in the battery lockers under the berth in La Reina. The Firefly batteries are also more sensitive to the charging so you have to have a smart regulator for the alternator and the shore power charger needs to be correctly set.
When this set of Lifeline batteries fail and I expect that to be sooner then later I will likely go with the Lifeline again since the switch will be easier (same size and same posts) although maybe by then lithium batteries will be more reasonable in price.
Hope that is of some help.
Mark Powers
La Reina 26C
Vancouver, B.C.
Good summary Mark. Only thing I would mention is AGM will accept a much higher charge rate so large capacity alternators and battery chargers are fully effective where with wet cells it takes a huge battery bank to "accept " much more than 50 amps after they are 60% full. So you can rebound faster with AGM’s vs wet cells.,
To the point I have my regulator set to throttle back my 120 amp alternator due to the single belt but I am not really losing much as the two golf cart wet cells can’t accept that much anyway. My 2 golf carts basically run the show and we get 8 years on a set, but they are lightly used as we do not have refrigeration.
AGMs do accept a higher charge rate but I have found it is not that much higher. My starter battery is usually full so is not really part of the equation. I have 2 105 amp AGMs making up the house bank. I also have a 75 amp alternator. When the batteries are down to 50%-60% and I start the engine the alternator will put in about 25 to 30 amps but it quickly drops to 18 amps. With batteries at 50% 6 hours of motoring will not bring them to full charge. I do not have a smart regulator nor a heat sensor. I might do better with those in place. The Firefly batteries are suppose to have higher acceptance rate then standard AGMs.
Considering the amount of time you spend on the boat each summer 8 years is probably the equivalent of my 13 years.
Mark Powers
La Reina 26C
Vancouver, B.C.
A smart 4 step regulator makes a material difference compared to the internal 2 steps ones. With the internal two step regulators they will be dropping off to 13.9 v in a matter of minutes. As well these regulators were designed to protect start batteries in a car engine where the ambient temps are much lower due to forced air ventilation. AGM deep cells and a hot alternator are a whole different game voltage wise Here is an interesting article on the subject
https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/
I use AGM batteries to power the Electric Propulsion system on my 30U Nonsuch. I love they are pretty much maintenance free. But, mine are never charged by an alternator connected to a diesel engine. They are only charged by a 120 volt battery charger and/or solar controller with an AGM charge profile which is slightly different than one used for flooded lead acids.
Mike
BIANKA
1986 30U
biankablog.blogspot.com
Been reading this email thread; my boat does have a diode isolator, (which may or may not be active) and an internal regulator.
I say that it “might not be active”, because one of the previous owners mentioned that the battery switch must be on “both” for both batteries to charge, which should not matter when using a diode isolator, unless the installer did some funky wiring. I had other things to think about after taking the reins this past September. (The prev. owners are/were a great help; I assume that the isolator wiring is old and pre-dates them, as wires are under other newer wires)
Anyway, something for me to think about next spring after launch; I’m not sure I want more than a 50amp alternator on my little W13, so maybe I’ll just remove the isolator, or figure out how to externally regulate the sucker. (or, just leave it and use the OEM 110v charger once in a while)
John - Cat’s Whiskers, NS26C #046
currently frozen to the ground in Kingston, ON.
Another option that hasn’t been mentioned: Lithium. VERY expensive but to me they were well worth it! When upgrading Adagio’s house bank from the cheap Wal Mart batteries the PO had installed we did a TON of research. We had all but decided to go with Trojan AGMs (3 x 100Ah) then we saw a sailing vlog that was extolling the virtues of Battleborn Lithiums. I looked them up and started reading about the pros and cons of going that route. We ended up getting 2 x 100Ah of their Group 27 “drop ins”. They have a BMS built in to each battery to keep the cells balanced, protect from overheat, over discharge and over charge. And it works! I know because somehow or another my charger profile was changed to wet and the batteries refused to take the long absorption charge it was trying to send. We were still able to draw power but not charge until I figured out what happened. They don’t require a special charger. We use an AGM charge profile and they charge FAST! They will suck every second out of the 20 amps my charger can put out until they are about 98% charged. then about 10 amps until done.
The great thing about Lithium, other than the higher max charge cycles (up to 5,000 according to the manufacturer but my research says closer to 3,000), is that you can draw them down to 0% depth of discharge with no harm. I talked to the manufacturer and they said the batteries actually contain more than the advertised 100Ah but the BMS only allows discharge of 100. We have ran ours down to 20% numerous times and they are sill putting out 12.7 volts+. They put out 13.2v until around 30% DOD accounting to my battery monitor. That was part of what sold us on them. The 3 Trojans would have provide ~150Ah usable. The two Battleborn lithiums provide 200Ah usable at about a third of the weight. The faster charging means more since we only have 200 watts of solar as well.
Here’s the con - for us at least. Technically you can charge them with an alternator BUT I have read countless articles that say you shouldn’t. Since they will accept up to 100 amps of charge current for so long they can start heating up your alternator fast which could lead to damage to the alternator. Because of that we rely on shore power, solar and generator to charge them exclusively. We just have to remember to switch the battery selector to the wet cell start battery bank when motoring.
They are an expensive option. We wouldn’t have sprung for them except we are full time livaboards and will be doing extensive cruising starting in a few weeks. We plan to avoid marinas as much as possible so will need to have the power available.
Just thought I would throw that out there since they weren’t mentioned.
Kevin Wilson
Adagio, NS30U #475
Biloxi, MS
Thanks for all the input. I wasn’t too concerned about the AGM starter battery because it’s not hooked to the charger or alternator. It only trickles from the house batteries and a 20 amp thermal circuit breaker keeps it from getting too much current.
I’ve decided to go with Chinese AGMs. Less than twice the price of flooded and half the price of Lifelines. If they’re no good, I should know within the one year warranty.
I’ll let you know how it works out.
One thing to consider when calculating charge times is the charge absorption rate. Lead-acid (of which AGM is a variant) are about 70-80%, the rest goes as heat. For example, 10A from the alternator for an hour will only add 7-8AH to the batteries. Another consideration is freezing. Our 58Kg (each!) Rolls batteries are too heavy to haul out every fall, one froze and a terminal is no longer level so its capacity is reduced. Next set of batteries will be individually lighter so that I can lift them out of the lazarette without subsequent hospitalization.
Alan & Tracy, “Corvus” NS30C, Toronto
Isolators are kinda old fashion and bring with them voltage drop issues. Combiners are readily available and do the job with the issues of voltage drop.
Using golf cart batteries to build your house bank has a few advantages,
cost is quite reasonable as there are lots of golf carts out there to power
they are readily available
you are splitting the weight into 60 lb or 33kg units so hauling then in and out if less of an issue
they seem to be robust, I have had 8 years each out of two sets so far ..16 years!
Bear in mind if you are leaving the batteries in the boat over the winter on a charger the charger needs to “temperature compensated” since charging voltages must change with temperature. In freezing temperatures changing voltage must rise to 14.4 v and at 0F close to 15v…otherwise the batteries will be not be charged. The reverse is true over 80F voltage should drop.
The other consideration is fire. Many marinas and YC do not permit boats to be plugged in while the facilities are unattended. Fibreglass burns in a very spectacular fashion and many yards have boats packed tightly together so there concerns have merit.