Battery Advice

[Mergatroid]

Noob owner of a 1994 h26. House battery is dead, I think. We are normal tailor sailors who do weekends, pretty low usage but I intend to add some fans, stereo but switch out the current lights with LED. Any ideas on what size battery I might need.

 

[Bill Roosa]

Power systems

You can't think of it as a battery or a load or a generator. You have to think of it as a load/storage/generator system.I'm going to make some assumptions to get us going. You day sail and don't intend to overnight. You have a shore power battery charger (20 amp) but no on board generator/alternator. You will want to plan for some additional loads as the comfort level grows.LoadsFans draw around 2 amps and you use them for 4 hours per day X 2 fans --> 16 Amp hoursStereos draw around 2 amps and you use it for 12 hours a day --> 24 Amp hoursNav lights draw around 3 amps for all three and you use it for 2 hours --> 6 Amp hoursCabin lights draw about 5 amps and you use them for 2 hours --> 10 Amp hoursAdding it all up you get 56 Amp hours each time you go out.Storage and rechargingThe worst case is if you sail on Friday night, Saturday and Sunday. With out getting really into it you would be using 56X2+56X.25=126 AH but you also would be charging each night. If you charge for 10 hours each night and you have a 20 amp charger that would be 200 amp hours back into the batts each night. This is more than enough to get them topped off before the next sail so all you need to store is the days usage or 56 AH. since you don't want to deeply (>50%) discharge your batteries as that makes them go bad faster you will need more than just 56 AH If you discharge to 50% then you would need twice the AH starting out or 112 AH.So I'm suggesting (based on the assumptions) that you need about 112 AH of battery bank. If you divide it between 2 batteries that is 2-56 AH deep cycle batteries. A lot depends on the size of your battery box. You can't get 10 lb of crap in a 5 lb bag no matter how much you want it to fit.Hope this helps.

 

[Mergatroid]

Thanks for the help

Thanks for the input.Only thing I would change is that we do spend some weekends on the boat.

 

[Jack h23.5]

Another viewpoint

I mostly daysail, and spend a few weekends aboard every year. I got tired of replacing the group 24 batteries, and now use a small 17 amp "jumpstart" type battery. I leave it home on the workbench to maintain its charge, and just plug the battery into the boat when I go sailing. I don't sail at night, so I generally have no usage from running lights. I only use the cabin lights when searching for things, and use a few candles or a rechargeable lantirn for cabin light. My GPS, VHF, Camera, TV, DVD, CD, Cell, Ipod, fans, and flashlights, all use rechargeable batteries anyway, so I set up a charging station to recharge the "AA's" at home or on board. I'm going on 7 years now with the same 17 amp jumpstart battery, and see no need for more. Also, every other night on the water is usually at a marina, where I can recharge my jumpstart if needed. This also allows me to move things around the boat without a lot of cords since most things are cordless. With that said, if I was going to run a refridgerator, or other high amperage devices, then yep, I'd need more power. Just thought I'd give you another benchmark.