Riddle me this about batteries

[Ronnie]

I may soon be replacing one of my interstate agm starting batteries which is currently being used as my house battery with a deep cycle battery but have a few questions that I’d bet you guys can help me out with:

1. What am I looking for in a deep cycle battery?
2. How do I tell what the “generic” Costco interstate batteries have in re Mca, Rc and amp hours?
3. Why do the starting batteries have a 42 month warranty but the deep cycles only 12 months?

In the pics The battery with leads on it is what’s installed currently. I have a spare generic battery also pictured but I don’t think it’s a deep cycle battery? It the black one pictured. The remaining interstates are what are offered by Costco right now. With the “dc” standing for deep cycle i assume.

 

[swatski]

Why do the starting batteries have a 42 month warranty but the deep cycles only 12 months?

Car batteries get charged w/everyday driving, or so they figure.
Of course if your deep cycle lives on a charger like mine it will live as long or longer.

--

 

[Gym]

I just bought an Interstate marine/RV battery. I had to go to an Interstate dealer to get it as most retailers like Walmart or Sears don't carry them. I just looked at the Costco site and only saw Interstate batteries for cars but not Marine. Does California Costco's offer marine grade batteries?

 

[jEt_jAk]

Swapped mine out for Odyssey ADM. So far so good.

 

[PaulyB]

For our boats, you don’t need many cranking amps. If you are only using it for starting, I would just buy the cheapest, these engines are designed to be started with small batteries for jet skis...

 

[Ronnie]

@Gym , the Costcos around me carry automotive (starting, green label) and rev/marine batteries (deep cycle, blue label), see my prior pics.

@jEt_jAk , not sure if you meant agm but that is what I currently have and am getting a “low aux volatage” warning on. These batteries are not that old and are on a charger maintainer most of the time.

@PaulyB , starting isn’t a problem for me as I have 2 starting batteries, which i paid a premium for at the interstate battery store. I’m trying to figure out if either of my deep cycle options at my local Costco is better than what I have currently installed. I hope so because Costco’s interstate batteries are a lot less expensive than those at the interstate battery store.

 

[Mainah]

I have had healthly debates on this topic here. IMO AGMs are the best for most people as both start and house. If you plan on running 4 amps, 4 subs, 4 towers, and 12 midranges then a large bank of golf cart deep cycles would fit the bill.

I installed a hydrohoist boat lift that I refurbished this weekend. Power was knocked out a few days ago when a different dock section was rippped off at my marina by a storm. I was still able to raise and lower the lift thanks both to my inverter and my dual group 31 AGM interstates. With the lift blower running it is pulling about 10 amps at 115v from the inverter. The inverter was pulling about 120 amps at 12.3v. I was able to raise and lower many times to try and get things situated. Oh yeah it was hot yesterday too. The batteries performed great and had 12.2v left when I wrapped up for the day. Try that with whatever batteries the dealer gave you.

They are also 2.5 years old and get well used by all of the stuff I have on board (ballast pumps, air pump, blender, kegerator, twin amp/sub stereo). Properly sized for use case agms are the best option for most boats and rvs IMO.

 

[PaulyB]

I have 4 AGM deep cycle batteries.... I bought my most recent ones from Sam's Club for 179. https://www.samsclub.com/sams/duracell-agm-deep-cycle-marine-and-rv-battery-group-size-31dtmagm/prod3590232.ip?sprodId=prod3590232&selectedTab=allProducts&_requestid=792499

They have 105 amp hr reserve capacity at 20 hrs, which seems to be almost the best you can find in a 12v battery.

 

[Ronnie]

I’m just trying to stop the low aux voltage alarm from coming back on and the stereo dying. The two interstate agm cranking batteries I bought 2 seasons ago (for about $500 total) were just confirmed to be fine by the interstate battery store yet the alarm comes on by the second day consequtive day on the water (I,e with one night with the bilge pump circuit on). This is why I replaced the stock batteries two years ago. Looks like I will end up on erring on the side of cost and caution and will buy the deep cycle battery recommended to me by the interstate store rep. I don’t know what this is yet but am sure it will be expensive and I certainly wish I would have taken his and @txav8r advice when I bought the AGMs years ago. That is buy one starting battery and one deep cycle (but no I had to have matching AGMs which seemed to have better specs than any deep cycle on the store’s shelves at the time).

 

[PaulyB]

SRM 29s are the best Deep cycle batts interstate makes, they are acid filled, not AGM's, and i think cost around 140.

 

[PaulyB]

How many house batteries are you using?

 

[Bruce]

@Ronnie, I doubt that a two year old AGM battery has failed.

Have you checked the voltage at the battery when the alarm is triggered? I suspect that the alarm or its connection may be faulty.

I have two Diehard Platinum group 31 AGM batteries in my boat. They were purchased at the end of 2013 and have served us well for 5 summers with no signs of any problems. They are connected to an on board charger and protected by a low voltage disconnect. They provide constant power to the refrigerator. These batteries are no longer available but were rebadged Odyssey batteries which remain available but punitively expensive. I expect that they will last many more years.

 

[Jgorm]

I've done lots of battery research for boats and RVs. For the house or aux battery, Trojan wet lead are the best. 6v vs 12 v is a toss up. You need to top them off a few times a year. If it's way hot, go agm. They cost more, and dont have as much capacity, but they can't run dry. Deep cycle batteries don't have the warranty because they know you'll abuse then by taking them below 50%. I use a current monitor to tell me how many amp hours I've used and let me know when i near 50%. There more times you go below 50% the faster the better dies. Take it below 10v more than a couple times and is trash. My rv came with walmart car batteries for the house me they will worked great for 5 years so I'm mixed in the benefit of the thick plate true deep cycle batteries. I use walmart for all lead batteries (premium) in all my vehicles . They have a legit warranty on u got 40 ea for 2 5yo batteries! Sealed is a must if the temps get 110+. I'm good with the wet sealed type or agm. I used to get Sears agm, but...

Keep all batteries on a 2+ stage charger, and never run them dead! Use a cutoff if need.

 

[Julian]

the alarm comes on by the second day consequtive day on the water

Do you have a big stereo and are cranking the tunes? I assume you have no overnight charging going on? Is your bilge pumping water, or just sensing for it?

 

[Ronnie]

I brought both batts in for testing a few weeks ago and they came back healthy per the interstate battery store. I have not checked the voltage at the battery when the alarm is triggered but I will bring a volt meter with me the next time I’m out. If the alarm or switch is the problem it sounds like I’m in it for more than the cost of a deep cycle battery.

In both instances when the alarm went off it was the second day on the water so no shore power to feed the onboard charger maintainer for one night .i don’t have a high powered sound system and only run one amp but rarely turn it up or leave it on for very long when at anchor or adrift. I turn the bilge pump on when the boat sits in the water overnight out of habit but it only checks for water every few minutes it does not actually come on and stay on.

I’m got a big credit at Costco so could buy a new deep cycle there but I also have a spare no name battery that is relatively new. Since I only plan one more overnight boating trip this year I may just replace my air start battery with the spare and see if that fixes the issue for the last trip gen deal with this again in the off season.

It would be nice to address this once and for all now but as usual I’m running out of time. I retro spect I didn’t have any alarm problems until I installed the speakers in the rear deck with leds built into them. Maybe I should disconnect the power to the less but they should not be drawing much power at all. Feels like I’m just grasping at straws now and may as well pray, do a rain dance, etc.

 

[Mainah]

I’m just trying to stop the low aux voltage alarm from coming back on and the stereo dying. The two interstate agm cranking batteries I bought 2 seasons ago (for about $500 total) were just confirmed to be fine by the interstate battery store yet the alarm comes on by the second day consequtive day on the water (I,e with one night with the bilge pump circuit on). This is why I replaced the stock batteries two years ago. Looks like I will end up on erring on the side of cost and caution and will buy the deep cycle battery recommended to me by the interstate store rep. I don’t know what this is yet but am sure it will be expensive and I certainly wish I would have taken his and @txav8r advice when I bought the AGMs years ago. That is buy one starting battery and one deep cycle (but no I had to have matching AGMs which seemed to have better specs than any deep cycle on the store’s shelves at the time).

Based upon the photos posted it appears as though you are using group 34 agm. A group 34 agm is referred to as a starting battery even though it is agm as its capacity is not all that much. A group 31 has 3x -4x the real world nominal voltage capacity of a group 34 in deep discharge. If it were me I would keep one or both of the group 34s as the start battery/bank, add a group 31 agm for the house, and make sure you do the DVSR mod. Keeping the batteries the same type is important because of the DVSR.

 

[Mainah]

Based upon the photos posted it appears as though you are using group 34 agm. A group 34 agm is referred to as a starting battery even though it is agm as its capacity is not all that much. A group 31 has 3x -4x the real world nominal voltage capacity of a group 34 in deep discharge. If it were me I would keep one or both of the group 34s as the start battery/bank, add a group 31 agm for the house, and make sure you do the DVSR mod. Keeping the batteries the same type is important because of the DVSR.

If you only use one group 34 for the start battery you could buy a ups device for something you want to run in a power outage at the house, remove the stock ups battery and connect the leads to the agm giving you hours instead of minutes of run time.

 

[Sbrown]

Man, you're really getting some interesting answers! First off, to eliminate some confusion, you can get either deep cycle or starting type batteries in just about any of the battery construction styles (lead acid, AGM, spiral wound, gel, etc). The generic style of construction does not dictate what the battery is used for other than, in any given construction style grouping, the deep cycle batteries are built differently internally than the same construction and group starting battery. I.E. a lead acid group 24 starting and a lead acid group 24 deep cycle are built differently internally even though they use the same construction material technology. Same goes for AGM and all the others. Your best bet is to use the same group size and construction for both batteries, but use a deep cycle for the house battery. Educate yourself to what the Reserve Capacity and Amp Hours actually mean, figure out how much reserve you really need, and then get batteries that are sufficient to handle the load and keep them isolated. Make sure your charging system is charging and occasionally put the deep cycle on a battery charger designed for a deep cycle battery. Deep cycle batteries cannot be recharged quickly and most charging systems that are engine driven are not capable of recharging a deep cycle battery properly.

Edited for some more info; I was doing some poking around on West Marine's site and decided to see what they had to say about batteries. They have a "dual purpose" battery that is supposed to work well for starting and deep cycle, although it doesn't do "deep cycle" as well as a purpose built deep cycle battery can. West Marine advisor seems pretty adamant about not mixing battery construction types. They say you MUST use batteries of the same type (lead acid, agm , gel etc)