Battery

[Capri]

Hello everyone. I recently bought a nice 1981 22'. I'm a little overwhelmed after reading about selecting a battery. I don't expect to require many amps initially. I have a depth finder (not sure if it's hooked up), the small galley light above sink, the light in the v berth, some 2 lights (not LED) on the spreaders, 2 lights on bow front, and one similar aft.

In the future I'd like to install a car cd player/stereo and small fan(s). I don't have a large budget. Which battery should i look at? I am clueless as to how I charge it? Once I get home?? I keep it in dry storage though. Do I need a solar panel to keep it charged? Also is there a gauge that can tell me how much power I have?

 

[Bill Roosa]

Depth sounder ~ 0.5 amps
galley light 1 amp
V birth light 1 amp
spreader lights 2 amps
navigation lights (bow and stern) 4 amps
anchor light (did not mention but bet you have one at the mast head) 1 amp
assumptions:
you will not have all these appliances on at the same time
your boat usage is the typical weekend with little night sailing, only to "get you there at the end of the day" use of the nav lights.
you will turn the lights on at dusk (1800) and off when you go to sleep.
you will leave the anchor light on all night (1800 to 0600)
Sooooo
you start at 0600 in the morning and turn on the depth sounder
you sail till 2000 turning on the nav lights at 1800 and off at 2000
you turn the anchor light on at 2000 and leave it on till 0600 the next morning
you have a refreshing beverage and dinner using the galley light from 2000 to 2300
and the V birth lights from 2030 to 2300
that completes Saturday.
depth sounder 0.5 amps for 14 hours (0600-2000)= 7 Amp hours (Ah)
nav lights 4 amps for 2 hours = 8 Ah
anchor light 1 amp for 10 hours = 10 Ah
galley light 1 amp for 3 hours = 3 Ah
V birth light 1 amp for 2.5 hours = 2.5 Ah
Total Ah usage from 0600 Saturday to 0600 Sunday = 7+8+10+3+2.5=30.5 Ah
I'll leave it to you to fill in the Sunday and Friday values. You would add them to the total usage above to figure our how much you are using over the weekend. For the 30.5 Ah above you would want at least a 61 Ah battery because you don't want to TOTALLY drain the batteries as that is really hard on them and massively shortens their life. Stick to 50% discharge.
You did not mention if you have a motor, solar, wind......charging capability. To simplify the though process think of loads as negative Ah and charging sources as positive Ah. Add the two together (algebraically) to see if you have net gain or loss from the batteries. Net gain is great assuming you have it before you drain the batts to 50%, a net loss is bad unless you want to leave the boat with dead batteries on Sunday and let the charger replenish them over the week days ......
I have a spread sheet that does most of the heavy lifting if you are interested.

 

[Capri]

This is exactly what I was looking for Mr. Roosa! Thank you. So, at the end of the trip it sounds like I take the battery home to charge because I don't have an alternator. That's my only option it sounds like. And how do I know if it's close to 50%?

 

[Stu Jackson]

The All-Important Energy Budget:

http://c34.org/bbs/index.php/topic,3976.0.html

 

[Bill Roosa]

Well, most auto batteries list Cold cranking amps (CCA) and reserver capacity (some amp draw for so many minutes). Real live marine deep cycle batteries list their Ah capacity. Most are around 100ish Ah, two of those 100 Ah would give your 200 Ah (wired in parallel of course as a series wiring would give you 12x2=24 volts output. If you know the battery make and model you can probably find the Ah by googling them (make, model, and"Amp hour". You DO NOT want an automotive battery as they are not designed to discharge to 50%. they get the car started and then the alternator supplies ALL the loads. They are designed to deliver a lot of power for a few seconds. Deep cycle marine batteries are designed to supply lower power (amps) for a long period of time.
knowing the state of charge (SOC) is a topic of many posts. If you play with the various boat electrical usages (scenarios?) you can get a range of Ah usages. Worst case it and buy enough battery storage to cover that scenario

 

[Capri]

Thanks to both of you.

 

[Benny17441]

You are asking about selecting a battery so I'll try to give you some of the basics. There are different types of batteries but I will recommend the basic lead/acid wet cell 12V Group 27 DEEP CYCLE battery. It stores about 110 Amp hours (Ah) and it is good for many cycles of discharge/charge. You can pick one up for around $90 at Walmarts. Check the Date of Manufacture and do not buy one that is older than 60-90 days. You may ask why do I recommend a battery without knowing your usage and needs and the answer is kind of simple, I was in your shoes once, 110Ah is as much as you are going to get for under $100 and I used to do weekends with a single battery just like that. You ask how do you know when your usage reaches 50% of capacity and the answer is you do not, you have to estimate the usage for 24 hour period.. Understand that the 50% threshold is not a steel gate that comes down and crushes the battery but a guideline just intended to extend the useful life of a battery. When you do your estimate always consider power conservation measures. A "C" Battery powered LED lamp can serve as a cockpit light and even an anchor light (your size boat does not require a mast mounted anchor light but you want to make sure you are seen) You do not have to use your fish finder for depth monitoring all the time, as you become familiar with the waters in your sailing area you may just turn it on at intervals to verify position and perhaps when you start getting close to shore. A Boom box with a CD player can provide music. Even more important than sticking to the 50% threshold is recharging the battery once you get done with your outing. I don't mean you have to run home but do not leave it in the boat to charge it the following day or week. The reason I like the cheaper wet cell batteries is that if one fails I can get off the boat and find a replacement real quick. I also do not feel as guilty when I have the need to abuse them a little. Just get your battery, use it as needed and always keep it charged. With no need for electrical power to start the outboard your sail should be worry free at least about the battery. Hope this helps until you learn as much about batteries and boat electrical system as you may want to learn. (never will get to know everything, as soon as you get close they change things and new stuff comes out)

 

[Capri]

Thank you, Benny. Your comments are incredibly helpful.

 

[Benny17441]

I forgot to mention warranties. Batteries are funky manufactured items; some can take a lot of abuse and practically refuse to die while others could die for no apparent reason in a few weeks. That is the reason for a warranty so that your initial investment is protected against early failure. I had recommended Walmart not only for price but also because they turn over the inventory rather fast and their batteries are usually fresh (under 60 days) and then in addition they seem to transfer their no hassle, no fault returns policy to the battery products. Do inquire about the product warranty and how long is the full price warranted and how long may the prorated portion last. Don't forget you are looking for Deep Cycle batteries and not Starting batteries nor Dual Purpose Batteries.

 

[Capri]

Excellent advice. Thank you.

 

[Ritdog]

I would also check out a 12 watt Powerfilm solar panel- my wife and I hung outs inside in a deadlight (window) and just trickle charged the battery during the week- they are about $250, but worth it. No regulator needed at that watttage.