Proper Battery for Sailboat

[weephee]

I just purchased two deep cycle batteries for my sailboat. They are 845 cranking amps each. I intend to use them for lighting as well as atomic 4 engine start. They will be connected in parallel and will be charged with the engine alternator and possibily a solar panel. Question is Is it ok to keep this type of battery (deep cycle) constantly charged via the alternator or is it the type that should be discharged before recharging. Maybe I purchased the wrong type of battery??? Are car batteries deep cycle. They are being constantly charged and don't last very long if completely discharged time and again. Thanks

[arf145]

Originally Posted by weephee

Is it ok to keep this type of battery (deep cycle) constantly charged via the alternator or is it the type that should be discharged before recharging. Maybe I purchased the wrong type of battery??? Are car batteries deep cycle. They are being constantly charged and don't last very long if completely discharged time and again. Thanks

Deep cycle batteries are happiest when kept charged up. Deeply/completely discharging them does damage, just as you say about car batts. There are a few types of deep cycles--lead acid wet cells, AGMs, gel--but they all are based on lead and acid, and none of them like hanging around discharged.

So you've got the correct batts if they are deep cycle, and I'm assuming they are standard wet type with fill caps? But if they are truly deep cycle, they will have an amp rating and not just a cranking amps rating.

[denverd0n]

Well, you already bought them, so it's a little late to be asking, but it does not sound like you got real deep cycle batteries, which rarely specify a CCA rating. My guess is that these are actually marine "dual-purpose" batteries, which are really meant for power boats that have some electrical use when the engine is off, but not all that much. Since you have them, you might as well use them. They will probably not last as long in deep cycle service as real deep cycle batteries would, but they will still be useful for some time.

In the future you want deep cycle batteries. You do not want ordinary car starting batteries. You also do not want dual-purpose batteries.

In any case, deep cycle batteries do not need to be discharged before recharging. They are not like the NiCd batteries in portable electronics that take a memory. Lead/acid batteries (whether they are wet, AGM, or gel) will all last longest if they are not too deeply discharged.

[weephee]

I looked at the batteries again and they are wet cell ie. caps to add distilled water and all that is on the label is 675 cold cranking amps and marine cranking amps @ 38 degrees F 845 Can I assume then that they are dual purpose rather than true deep cycle batteries. They were sold as deep cycle at Cosco.

[SVPrairieRose]

Well, I would look into returning one of the two batteries as they are not truly deep cycle. Being a Costco purchase I would expect that they take them back especially if you make a stink about the fact that they are not what they said they were. Now once you get rid of one I would replace it with a true deep cycle flooded battery, I assume your power needs ares small so a group 27 might do you well, but that is your decision to make. Now to install them please don't have just one bank, use the Costco battery for starting and the de ep cycle for all other loads, you can use a selector switch to change between banks for draw and charging but would be better to set up a slightly more sophisticated system that will draw from the start battery when starting and run your lights and electronics from the house bank and charge the batteries as needed with no switching required. In the system you describe a dead battery is likely to leave you engineless whereas this system makes that scenario virtually impossible.
This is what you want, or at least what I would do in your position.

Add a Battery - Blue Sea Systems

[arf145]

Originally Posted by weephee

I looked at the batteries again and they are wet cell ie. caps to add distilled water and all that is on the label is 675 cold cranking amps and marine cranking amps @ 38 degrees F 845 Can I assume then that they are dual purpose rather than true deep cycle batteries. They were sold as deep cycle at Cosco.

My deep cycle batts are from Costco. Do yours actually say "Deep Cycle" on them? If so, those really are deep cycles. At my Costco, they had Group 24 deep cycles, and Group 27 dual purpose. The deep cycles did give an amp hour rating of 85 I believe. I also have a Cosco Group 27 marine dual-purpose battery as my backup spare, because it just sits there charged up all the time and won't see much cycling.

If you haven't done anything to them and you've got the wrong ones, they might take them back. Won't be the end of the world if they don't or you can't. They won't last as long as deep cycles if drawn down a lot.

[weephee]

Thanks for the replies. I'll look into returning one of them. Now I know the difference. Thanks again

[delite]

Be careful about mixing battery types as some charge at different rates and can be damaged. A good charger will be able to handle different battery types.

[ccriders]

Consider returning both and getting two group 27 deep cycle batteries. A deep cycle battery has plenty of cranking amps for an Atomic Four engine and then you will have two identical batteries to care for and not have to worry about which switch position you are in. Just run battery to the discharge level you want and then switch to the second. I have had this setup on my boat for three years now and it works fine.
High cranking amps are required for diesels and large gasonline engines, but not for the Atomic Four.
Also, a battery charger designed for two batteries and wired directly to the batteries allows you to completely turn off your DC circuits while away from the boat and charge the batteries at the same time.
John

[TQA]

A lot of people have a dedicated engine starting battery which for an A4 could be quite small and a deep cycle battery [house] for everything else. Your charging system needs to be slighly nore sophisticated to prevent the house battery from "stealing" current from the starting battery. This way even if you run your house battery flat,, and you will do, you can still start the engine. It is possible to do this with a manual switch but inevitably one day you forget and then find yourself with two flat batteries.