Am I killing my batteries?

[dave_and_dd]

Ok, I've been reading around on here, read (not necessarily understood) Mr. MainSail's musings (wow... lotsa good info!) and article's like "Battery Voltage vs State of Charge"....and I'm pretty confused. But here's my situation:

Weekend sailor. only once in a grand while doing any overnight cruising at this point in our lives. We usually sail about 4 hours almost every week. Catalina 309. One 4D and one group 27 flooded batts. 55AMP alternator. Usually start and run on 4D batt only, head out about 20 min much of which is at 3k rpms, then sail several hours with vhf, gps, nav instruments (and rarely use autopilot). Then start up and head back in (20 min / approx 3krpm for much of it).

Every 4 to 5 weeks I start on the group 27 battery to see that is is working, when I do, after starting, I switch the batts to both for charging - never starting on both.

The batteries seem to be maintaining using the above procedures.

My question: is that going to harm them? I have a Blue Seas charger (P12 - 25amp), but have rarely used it. Do I need to add a "once a month" full additional charge cycle all the way to float on the Blue Seas to keep the batts healthy?

Thanks for any insight - David - Tampa, FL

 

[Tom J]

Is the group 27 a start battery? If so, you might do better to routinely start the engine with the group 27, switch to both for charging, and save the 4D for the house, assuming the 4D is a deep cycle.

 

[Benny17441]

David a few things, you have two different size batteries and I would suspect they may be of different age. Not a problem if both batteries are good and used independently but they would not match well for combining them. At some point the mismatch or a faltering battery would drag down the healthier one. Just give some consideration when it is time to replace a battery(s) to make both the same. For your usage two group 27 deep cycle batteries would do nicely and you could alternate their use for each outing keeping them both equally active. The other thing is that you seem to be making an assumption that by motoring 20 minutes at the end of the day that your batteries get fully charged and that is likely not the case. As batteries approach 90% of charge the battery acceptance of the charging current diminishes significantly and it may likely take an hour or more just to top them off. Leaving a battery not fully charged for a length of time makes it susceptible to sulfating which will reduce its capacity to hold charge as well as its useful life. You have a good charger so turn it on as soon as you get back to port and finish charging both batteries. You can leave the charger on 24/7 as when the charge cycle is fully done it will go into a float cycle just to maintain charge. Some recommend disconnecting the charger at least once a week for 24 hours to allow the batteries to rest but I would add, "only if convenient" as the benefits will not be very significant. Cruisers and sailor with high power loads will need more sophisticated battery systems and monitors but for light duty what you got is very adequate.

 

[Maine Sail]

One 4D and one group 27 flooded batts. 55AMP alternator. Usually start and run on 4D batt only, head out about 20 min much of which is at 3k rpms, then sail several hours with vhf, gps, nav instruments (and rarely use autopilot). Then start up and head back in (20 min / approx 3krpm for much of it).

This is cake walk for a 4D battery provided it is fully recharged after being discharged.

Every 4 to 5 weeks I start on the group 27 battery to see that is is working, when I do, after starting, I switch the batts to both for charging - never starting on both.

Never a bad idea to test the start battery occasionally. You are fine to start & charge on BOTH/PARALLEL, if you want to. This avoids switching when the engine is running. It should not be necessary to use BOTH to start, this would mean one bank was weak, but you can start on BOTH just don't let it become a Band-Aid hiding a battery bank problem..

The key is to not "discharge" the batteries in parallel so this means switching back to the 4D when you shut off the engine.

The batteries seem to be maintaining using the above procedures.

You're not really deeply discharging them but you are also not fully recharging them...

My question: is that going to harm them? I have a Blue Seas charger (P12 - 25amp), but have rarely used it. Do I need to add a "once a month" full additional charge cycle all the way to float on the Blue Seas to keep the batts healthy?

If you are at a dock, for storage, use your Blue Sea charger 24/7. The self discharge in sunny Florida, and not getting back to 100% SOC, with an alternator this can take 7+ hours or more, means you can be harming your batteries. You are not harming them badly by your depth of discharge but by not getting them back to 100% SOC you are damaging them.

The Blue Sea P12 is an excellent charger don't be afraid to use it at the dock.. If you are on a mooring get solar...

 

[Maine Sail]

Is the group 27 a start battery? If so, you might do better to routinely start the engine with the group 27, switch to both for charging, and save the 4D for the house, assuming the 4D is a deep cycle.

There are only two battery manufacturers I know of who actually make a flooded 4D deep cycle battery. Dyno Battery in Washington state and Rolls battery. All other 4D flooded batteries are DINO's or deep cycle in name only or put another way LIARS......

At best the 4D & 8D's batteries we get are a dual purpose battery and at the worst a 4D or 8D starting battery with a deep cycle sticker slapped on it.

What is a Deep Cycle Battery? (LINK)

 

[dave_and_dd]

Thanks for all the replies folks....
I am at a dock with shore power. I was somehow trepidatious of just leaving the Blue Seas charger on for 7 days at a time between times I'm out there sailing.

....If you are at a dock, for storage, use your Blue Sea charger 24/7.....
The Blue Sea P12 is an excellent charger don't be afraid to use it at the dock.. If you are on a mooring get solar...

If that's the better thing to do, that's what I shall.
And I'll check out the brand/label on the house battery next time I'm there, but as you say, I suspect it is a LIAR....

Thanks all - David