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Just starting out, have questions about charging the battery

Apr 4, 2019
Hunter 27-2 Kerr Lake, NC
Went out on my boat this weekend for the first time -- a Hunter 27. At the dock before leaving, I hooked the battery (12V deep cycle) up to the charger. When I started charging it it read 35% and then pretty quickly got up to 45% but then stopped. I left it connected while we got the boat ready, but then decided to head out. It's not a huge lake, and the weather was calm so I wasn't worried about the prospect of losing power while on the lake.

During the sail, I had the cabin lights (panel only -- lights themselves were off), the depth finder, and the VHF turned on but nothing else. Before two hours of sailing, we lost all power.

Back at the dock, plugged the battery back into the charger and it immediately read 35% again (I expected it to be lower), and I was able to get it up to 47% this time before we had to leave. Disconnected the charger and all lights/power were working before I turned off the switches on the panel and locked it up.

Does it sound like the battery itself is bad? Does it just need a much longer time to charge? Total noob to all this, so I'm not sure what I should be expecting. Thanks!

One more question:

I've read different info on whether I should remove the battery while charging it. I did not remove/disconnect the battery while charging. I'm using a Schumacher SC-1200 to charge it, and I just hooked black to black and red to red. Anything wrong there?
Jul 7, 2004
Hunter 30T Cheney, KS
Sounds like the battery is bad but I'm no expert. Did you check the water level in it?
The charger hookup sounds right
Apr 4, 2019
Hunter 27-2 Kerr Lake, NC
Leaving them partially charged is a good way to kill the batteries.
Thanks. That ship sailed (pun intended) when I bought the boat. This weekend was the first chance I had to get into the boat and check stuff like this. The boat came with a small solar panel. Should I just leave that connected at all times? I suspect I could pretty easily just mount it off the rail at the transom.
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME
First problem is a Schumacher charger. These should really not be used on a boat. You'll want a "multi-stage marine charger" that can do bulk, absorption & float. Second is you're not allowing it to charge long enough. It can take 10 hours & many times much longer for batteries to charge. Third, your batteries may well be expired and beyond their useful life....
Dec 23, 2016
Catalina 27 Clinton CT
Check the water level, date of manufacture. Let it charge until full, then load test it to see what is going on.
Jul 7, 2004
Hunter 30T Cheney, KS
Might be best to take the charger and battery home to charge overnight. Is a single battery enough for all your needs plus starting the engine?
Apr 4, 2019
Hunter 27-2 Kerr Lake, NC
First problem is a Schumacher charger. These should really not be used on a boat.
Why is that? It's not a permanent fixture. I don't have shore power so it's used as a temporary measure when I'm there and can run an extension cord. It has settings for deep cycle, so why wouldn't it be suitable just for charging?

Is a single battery enough for all your needs plus starting the engine?
The motor is an outboard with a pull cord for starting. The battery only handles the lights, depth finder, VHF, and bilge pump (currently set to auto). It's that last one I'm most worried about since I'd hate for it to be out of commission when it's rainy in case of any leaks. Boat seems to be pretty dry inside, but still.

Thanks for all the tips. I think next time I have about a week of dry weather in the forecast (where I'm not worried about rain seeping in) I'll pull the battery, bring it home, and try to charge it for longer and see how it goes. It's just tough to get to the marina except on weekends. Worst case, I need a new battery. And I'll look into hooking up the solar panel to keep a charge on it while I'm away.
May 24, 2004
CC 30 South Florida
To recharge a battery may take from 5 to 10 hours depending on the size of the charger. As the charge builds up in a battery the capacity of the battery to accept charge diminishes. I would recommend you first determine if the battery is good, take it to an auto parts store and have it checked with a computerized tester. If the battery is good charge it at home overnight. The use of the battery will dictate what type of battery you should be using. If it is to start an engine you may consider a starting battery but if the house is to provide house power to lights and appliances then you need a deep cycle battery. Small diesel engines can be cranked by a Deep Cycle battery so one of these could provide dual service safely. A starting battery would soon be damaged if used for deep cycling. Deep cycle batteries are rated in Ah and they range usually between 90Ah and 110Ah. Batteries should not be discharged beyond 50% to maintain a reasonable useful life. So if you consume 40 Ah in a single outing you will have to put them back with the charger. Batteries loose capacity over time and some may only reach full charge at 90% of its original capacity. A battery that will only charge to 50% of its original capacity is considered dead. The topic of batteries is long so start with the basics about choosing the best battery for your needs and learn how to take care of it. A wet cell battery should not be allowed to remain partially discharged as sulfation will kill it. We have inboard smart chargers in our boats and as long as the boat is docked we keep the charger on 24/7. I would not keep an alligators clip charger unattended and I do not know what type of charger you have but use one approved for marine use.

Ward H

Nov 7, 2011
Catalina 30 Mk II Barnegat, NJ
Welcome to the forum and to sailing!
There's a whole science to batteries and charging but since your starting out, I suggest you don't worry about that at this point.
If you battery was decently charged and in good shape it should have powered your VHF and depth sounder for many hours.
Take the advice to have the battery tested. If bad, replace, if good, give it a good 24 hour charge. The solar panel, if it is a decent size, should maintain your battery since it sounds like you only sail on the weekend and your use is light.
A battery does not need to be removed from a boat to be charged but in your case, without shore power and a marine rated charger, it may be better to take it home once in a while to give it a good overnight charge.

Enjoy your new boat!
  • Like
Likes: Scott T-Bird
Jan 25, 2011
S2 11.0A Anacortes, WA
Mainsail gave you some good advice. I would suggest doing some reading and learning about batteries and charging. His “marine how to” site is excellent. The Catalina groups also have good reading. Perhaps Stu can provide some links. Some searching on this forum will also provide numerous links to info. If you want to be knowledgeable, you have spend the time..
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Likes: StargazerP303
Oct 26, 2008
Starwind 27 Barnegat, NJ
I don't think that I would place any stock in a readout on the charger for the state of charge on the battery. I doubt it has any accuracy because I don't know how it could have any reference point for the state of charge. It probably responds to the charge acceptance rate and basically makes an assumption. You can't make any determination of the battery's condition based on the read-out from the charger. If your battery is bad and basically has very little capacity, the charger may eventually read 90% if it is left charging long enough. It won't necessarily mean that your battery has any reasonable capacity. Ward is right … your battery went dead long before it should have. I'd bet that your battery has been chronically undercharged.

Well, it's a good thing that you don't leave the battery charging when you are not around. You should never do that with this type of charger. If the boat is new to you, and you don't know how long the previous owner chronically abused the battery by systematically under charging it, you probably have a battery that is very close to the end of its usefulness. Be prepared when you purchase new batteries. Read all of the references that have been suggested and stay tuned to the forum topics so you know how to maintain your new batteries, before you abuse them to death yourself. On a sailboat, where you will need to be operating with deep-cycle batteries, it is no simple thing to maintain the proper charge for longer battery life.

Be forewarned. You will open a door to a whole new world of electricity. It's easy to get carried away! :)
  • Like
Likes: jssailem
May 20, 2016
Catalina 36 MK1 94 Everett, WA
One word of warning .... solar panels even small ones will overcharge and ruin batteries if they are connected directly to the Battery. You need to have a controller (mppt or pwm)
Apr 4, 2019
Hunter 27-2 Kerr Lake, NC
Thanks again to everyone for the help. I've been reading up, and yeah... I think this battery is likely shot. I will pull it, get it tested (and likely replaced), and then install the solar panel I have (or a better one if the one I have is not up to snuff) with a controller to keep it topped off while I'm away from the boat.