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 Basic battery charger/tender?
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Initially Posted - 10/03/2021 :  07:31:00  Show Profile  Reply with Quote
Greetings from TX, where itís finally cooling off enough for some fun fall sailing!
After (ahem) ignoring my boat for over a month, Iíve found that the battery is not at full charge. It was brand new when I bought the boat 2 years ago and is an Everstart 12v lead acid starting battery from Walmart, Group 24ms, 625 mca. I rarely need to use lights or other electrical systems as Iím only a day sailor on a lake. Itís mostly used to start the outboard and run its hydraulic lift and occasionally to charge up my portable speaker from the auxiliary cigarette lighter.
Can anyone suggest a basic battery charger/tender that I could plug into the marinaís power outlet (not a shore power plug, just a plain outlet) with an extension cord? Bonus points if the charger plugs into the cigarette lighter vs. having to connect to the battery itself.
I apologize if this seems very elementaryÖ I am fairly new at this and definitely not experienced in electrical systems and donít want to get in over my head. Iíve read through a ton of posts on this forum about batteries and honestly donít understand most of the technical discussions.
Thank you!

2004 C250WK #750 Waco, TX


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Response Posted - 10/03/2021 :  11:41:42  Show Profile  Reply with Quote
I use a small solar panel to keep my battery topped up. It works great.

Amber Waves
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Steve Milby
Past Commodore

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Response Posted - 10/03/2021 :  13:14:03  Show Profile  Reply with Quote
I used a small solar charger on my Cal 25 and really liked it. I wired it to plug into the lighter outlet. The only drawback was that I didn't make the wiring robust enough, and the wires broke. You don't have to run an extension cord to a dock outlet. Just plug it into the lighter outlet. Also, you can recharge your battery when away from the dock.

I have used different brands of battery tenders and haven't seen any appreciable difference among them. They all work well.

If you ever have to replace your battery, I suggest you replace it with a deep cycle battery, instead of a starter battery. I used a deep cycle battery to start the 35 hp diesel engine in my C&C 35 and it worked well, and outlasted starter batteries. A deep cycle battery has ample cranking amps to start your motor. A battery on a boat usually gets deeply discharged frequently, and starter batteries don't tolerate deep discharging very well. A deep cycle battery tolerates it much better.

Steve Milby C&C 35 Landfall ("Captiva Wind"); Cal 25 ("FahrvergnŁgen")
Past Commodore
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Response Posted - 10/04/2021 :  05:07:09  Show Profile  Reply with Quote
Ellen, 1) batteries should not remain discharged for any length of time or they will loose their ability to recharge effectively, 2) as you have discovered, a battery will self discharge even with no external load (current draw) especially in hot environments, and 3) except in an emergency situation, you should not discharge your battery below 50% state of charge. Fortunately, you can approximate state of charge simply by monitoring the battery voltage with no load (all switches off). Google battery voltage chart but basically your battery should be maintained between about 12.1 (50% SoC) and 12.6 Volts (100% SoC).

So....first get yourself a volt meter so you can regularly monitor your batteries state of charge. Look on Amazon or your local auto parts store but you can find affordable digital models that simply plug into a DC outlet. Someone here on the forum will hopefully point you to their favorites. Note, however, for a reasonably accurate reading, you observe the voltage after the battery has rested 1-24hrs after being charged and with no load.

As for charging/maintaining your battery, you have various options. First, if your battery is seriously discharged I would recommend taking it home if you have a charger or to a professional garage and charging it overnight. If it is only moderately discharged, then if your outboard has an alternator and is wired to your battery, than perhaps 20-30 minutes of motoring would notably help and a few minutes each outing could notably contribute to keeping your battery charged. Secondly, as already noted, a small (5 Watt) solar charger (sometimes referred to as a trickle charger) is an easy way to maintain and recharge a battery that receives light use. They are small, affordable and do not require a charge controller. They do require an in-line fuse, although that should come with the charger. Depending upon the weather, the amount your battery is discharged and whether the panel is exposed to full sun or not, it may take one-to-a few days to recharge a fully (50%) discharged battery but unless you are sailing most every day these work great and there is no need to be concerned about battery self discharge. As was suggested, you can charge through an existing DC outlet or they can be easily wired directly to your battery. I installed a two-prong DC external connection in the cockpit and hang the panel on the stern railing using a RAM mount for maximum solar exposure but you could also simply set the panel on the cockpit seat at the cost of somewhat less exposure. At your latitude, however, you likely have plenty of sunlight. Lastly, you could go with a dedicated charger but for your needs, I wouldn't go there. For safety reasons, I especially would hesitate about using an extension cord running to a typical, i.e. non-marine/not GFCI protected outlet. AC and water do not play well together.

One last suggestion, for your own use, some rainy day do a simple energy budget for your boat. Sum the current draw (Amps x hours of use) of each of your loads (speaker, lights, etc.) to get a ballpark feel for a days-use battery draw. Fixtures typically are stamped with their Wattage where Watts = Volts x Amps or you can find estimates for similar items on-line or ask here on the forum. You should also then estimate how long it should take to recharge that daily draw using your outboard vs. your solar panel. For the latter, typically assume 50% of maximum (advertised) efficiency. Many here on the forum can help if needed.

Good luck and let us know how it goes.

Gerry & Leslie; Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #597
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