Deep cycle or dual purpose batteries?

[bsangs]

Went down an internet marine battery rabbit hole, and after coming up for air, thought it'd be best to rest here.

Am going to replace my two batteries come March. Current ones were installed by previous owner and they're about five years old. They're also just run-of-the-mill Diehard Heavy Duty batteries. I'm planning to get a couple AGM marine batteries, Group 27 or 31.

What I can't settle on is if I should choose deep cycle or dual purpose. Don't need a separate starter battery, since these will run in parallel through my battery switch. CCA required for my Yanmar 3GM30F is pretty low, so either type should be able to handle firing her up. Still have a 55 amp alternator, 200 watt solar panel, shore power recharger, etc. Electronics are mainly water pump, GPS (new radar being installed soon), AIS, fridge, running lights, cabin lights, electric head and stereo/Sirius XM receiver. The occasional electric windlass, and anchor wash down pump too. What say the Ericson crowd when it comes to deep cycle or dual purpose? And can I assume most name brands are similar in output/performance? Or are there brands to avoid?

***Just an FYI, am NOT interested in converting to Lithium batteries at this time, so no need to throw those into the mix here. *** Thanks as always.

 

[Christian Williams]

I knew zero about "dual purpose," so I Googled it vs. deep cycle. I still know zero, after worlds of contradictory blather. Perhaps there is zero to know? But I await instruction.

FWIW, my AGM 31 deep cycles start the engine fine, even with some occasional very long cranking, and have lasted eight years. They're kept at 100 percent by shore power. So that works for me.

 

[bsangs]

"Contradictory blather." Perfectly worded Christian.

 

[Kenneth K]

Even deeply researching "deep cycle" batteries becomes a rabbit hole. Many claim that deep cycle batteries have thicker plates, and that below a certain thickness, many batteries that claim to be deep cycle actually fail that particular threshold.

Still, there is no real need for "dual purpose" batteries as deep cycle batteries are just fine for cranking. There is a need for deep cycling on most boats though, and that's something most cranking batteries aren't built for. I'd go for the deep-cycle batteries.

 

[bsangs]

Good. Deep cycle is where I was leaning anyway. Sounds like dual purpose is some nice marketing jargon that leads to confusion. Thanks.

 

[KS Dave]

I recommend Maine Sail's Article on this topic - What is a Deep Cycle Battery?

While it's a few years old, lots of good info in here to clear up the marketing fluff.

Personally, I have a couple of the "dual purpose" batteries that get me by, mostly because it's what came with the boat. I'm a lake sailor, so my electrical needs are pretty low. The E26, by default, uses a Group 24 battery, so that limits how much I can do with a true deep cycle battery.

 

[bgary]

Went down an internet marine battery rabbit hole, and after coming up for air, thought it'd be best to rest here.

A couple of years ago I went down that same rabbit hole and ended up posting my aggregated "learnings" here:

Battery Kindergarten (part 1 of 3) Types, charging, maintenance

I sent myself to Battery Kindergarten yesterday - spent the day with a few books in hopes of raising my boat-IQ a few points (Hey, it's worth a shot). Parking a bunch of tidbits here mostly to bookmark what (I think) I've learned, so that I can...

ericsonyachts.org

Battery Kindergarten (Part 2 of 3) Testing, problems, equalization

(continued from Part 1) Battery Testing Five kinds of testing 1: Open-Circuit Voltage Open circuit means no current in, no current out Battery switch to OFF Battery charger not sending any current (shore-power disconnected?) Anything...

ericsonyachts.org

E32-3 - Battery Kindergarten (part 3 of 3) Best practices and sources

Best practices Discharge Floor As a rule of thumb, limit discharge to 50% of capacity don't pull more than 50Ah from a 100Ah battery Don't allow no-load/rested voltage to drop below 12.0V Going lower will shorten the life of the battery...

ericsonyachts.org

(sure, let's be charitable and pretend I learned something)

I personal think "dual purpose" is marketing-speak for a compromise... it seems to me that for our purposes deep-cycle is the right way to go. ymmv.

Bruce

 

[Loren Beach]

I personal think "dual purpose" is marketing-speak for a compromise... it seems to me that for our purposes deep-cycle is the right way to go. ymmv.

"The duck just came down...."

 

[peaman]

I personal think "dual purpose" is marketing-speak for a compromise... it seems to me that for our purposes deep-cycle is the right way to go. ymmv.

Jack of all trades, master of none.

I got deep cycle house batteries, but I also have dedicated start and house.

 

[bsangs]

Think I'm going to be limited to traditional lead acid replacement batteries, if I understand my on-board charger's limitations properly anyway. Its float charge profile is 13.4 and I'll be damned if I can find any deep cycle AGM batteries that don't require a 13.6 float. This is an old ProMariner ProSport charger that requires different color caps to be changed in order to switch the battery profile, and those caps cannot be found anywhere - on my boat, or from ProMariner. (If you're thinking that's a dumb concept, you are not alone.) So I'm limited to the default profile, which is for lead acid batteries. Oh well. They're cheaper anyway.

 

[Frank Langer]

It's my understanding that flooded wet cell batteries gas off during charging, and therefore require venting to meet ABYC standards. On many Ericson boats the batteries are inside the boat in a closed locker, sometimes under the quarter berth where someone may sleep.
I have AGM batteries that apparently don't require venting.
I've been amazed that no surveyor has ever asked about battery storage location, even though the need for venting is often mentioned in articles about batteries.
Frank

 

[KS Dave]

So I'm limited to the default profile, which is for lead acid batteries. Oh well. They're cheaper anyway.

Have you thought about replacing your battery charger? I have an old crusty Guest ChargePro from 2001 and I'm thinking about ditching it, for multiple reasons. You can get a modern charger for $150. The Victron Energy Blue Smart IP65 12-Volt 15 amp. It's smart and would let you grow into lots of battery chemistries.

 

[bsangs]

Have you thought about replacing your battery charger? I have an old crusty Guest ChargePro from 2001 and I'm thinking about ditching it, for multiple reasons. You can get a modern charger for $150. The Victron Energy Blue Smart IP65 12-Volt 15 amp. It's smart and would let you grow into lots of battery chemistries.

No, I haven't for a couple reasons. It works perfectly fine with my current batteries, and it was installed in such a pain in the ass location that I cannot bear the thought of changing it out unless it breaks. I don't know which of the previous owners installed it where it is, but they must have employed a tiny dexterous child to do so, or stripped out the entire exhaust system and hot water heater so it could be attached to the far wall, when entering via the cockpit lazarette. But, if I have to, I will. My batteries are still working fine (knock wood), but I realize I'm tempting fate with their age and need to have replacements at the ready. And if I could somehow find the correct profile plug cap, I'd be able to use all battery types but Lithium.

 

[Prairie Schooner]

Think I'm going to be limited to traditional lead acid replacement batteries, if I understand my on-board charger's limitations properly anyway. Its float charge profile is 13.4 and I'll be damned if I can find any deep cycle AGM batteries that don't require a 13.6 float. This is an old ProMariner ProSport charger that requires different color caps to be changed in order to switch the battery profile, and those caps cannot be found anywhere - on my boat, or from ProMariner. (If you're thinking that's a dumb concept, you are not alone.) So I'm limited to the default profile, which is for lead acid batteries. Oh well. They're cheaper anyway.

We've put in AGMs about 18 months ago. Our boat came with a Balmar alternator and regulator and wet lead batteries. I'm really lame on electrics and didn't find out until late last season that we need to adjust the regulator for the AGMs. The system seemed to work okay with the old settings, but we may have been doing long term damage. Haven't done it yet, but thanks for the reminder, Brian.

 

[KS Dave]

No, I haven't for a couple reasons. It works perfectly fine with my current batteries, and it was installed in such a pain in the ass location that I cannot bear the thought of changing it out unless it breaks.

Fair enough! Mine is in a hard place, too. I have to reach across the top of the engine, under the cockpit, in a space that is too thin for how thick I am across the middle. I think this one should be smaller enough to fit elsewhere as it's a "portable" charger, but can still be mounted somewhere.

 

[bsangs]

We've put in AGMs about 18 months ago. Our boat came with a Balmar alternator and regulator and wet lead batteries. I'm really lame on electrics and didn't find out until late last season that we need to adjust the regulator for the AGMs. The system seemed to work okay with the old settings, but we may have been doing long term damage. Haven't done it yet, but thanks for the reminder, Brian.

Well of course it's my pleasure, Jeff.

Think I'm just going to swap out the current batteries for the same model. Keep things simple. They're DieHard Heavy Duty batteries, used primarily for farm and truck equipment. Group 31 so they're big suckers with a high CCA and reserve capacity, and they've certainly worked well for nearly five years, so no reason to think new ones won't. They don't break the Boat Bucks Bank too much either.

 

[bigd14]

I've been amazed that no surveyor has ever asked about battery storage location, even though the need for venting is often mentioned in articles about batteries.
Frank

I have often wondered about this. I do sometimes get a whiff of battery charging gas (two lead acid golf cart batteries). Thousands of boats must have similar arrangements and I don’t hear about too many of them spontaneously combusting from it, so I have chosen not to worry about it. I figure the lid and the old wiring holes and the generally porous nature of the aft end of the boat is enough to keep the gas from concentrating too much. Unfortunately though, there is a ton of wiring right next to the batteries, but it’s new wiring, so I just hope for no sparkiness.

 

[Christian Williams]

My PO fried $1200 worth of batteries using this ancient charger. He said he was attached to it. My electrician put in a modern charger ($200 at the time) and the new AGMS have been good since 2016.

Beware emotional attachment to electronic gizmos. Or anything without a pulse.

 

[southofvictor]

We've put in AGMs about 18 months ago. Our boat came with a Balmar alternator and regulator and wet lead batteries. I'm really lame on electrics and didn't find out until late last season that we need to adjust the regulator for the AGMs. The system seemed to work okay with the old settings, but we may have been doing long term damage. Haven't done it yet, but thanks for the reminder, Brian.

if you’re fully charging them you shouldnt have done any damage, you’ve just taken longer to charge them than you would have with an AGM profile absorption voltage like 14.4 or 14.6v.

 

[southofvictor]

My PO fried $1200 worth of batteries using this ancient charger. He said he was attached to it. My electrician put in a modern charger ($200 at the time) and the new AGMS have been good since 2016.

You should put that thing on the wall!