SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

dual battery setup.

2K views 16 replies 7 participants last post by  dorourke 
#1 ·
I needed to replace my batteries, they were old and not chargable any more. I ran to West Marine to get one to start the engine. I bought a West Marine Sea Volt Deep Cycle 75 amps per hour. Do I need to have the same type battery for the second one, or can I get away with a cheeper and less performing one?
 
#3 ·
If they're going to be part of a single battery bank, then you really should get two of the same batteries to reduce problems caused by different charging/discharging rates. If they're going to be separate banks, then you can get a different battery, but I would stick with the same type of battery—if you have a wet cell, get another wet cell, etc...

75 Amp-Hours is a pretty small house bank, and unless you are running your engine all the time to re-charge the batteries or don't use much in the way of electronics, you probably want to get more capacity in your house bank.

It would help if you said what kind of boat you have as well as what kind of charging capabilities you have aboard—high-capacity alternator, wind generator, solar panels, etc.
 
#4 ·
OK. My boat is an S2 8.0B with an alternator and full charging capabilities. I only plan to use limited electrical, such as nav lights and radio when needed. So Sailingdog, what youre saying is if I get a lesser battery for my dual setup then the lesser battery might draw power from my better one when I use the both switch? I know the setup is in parralel. Woulden't it be like two gas tanks? The maine a higher octane with more capacity and the reserve with a lower grade as well as a smaller capacity?
 
#5 ·
What I'm saying is that the batteries in a single battery bank should be of equal size age and chemistry type. If you mix battery sizes, the smaller battery will likely be overcharged and overdrawn much of the time... leading to a vastly shortened battery life. If you mix battery chemistries, then a wet-cell may not be fully charged while an AGM in the same bank is close to fully charged, since they have different charge acceptance rates due to their different chemistries.

If you have two separate battery banks, and only combine them in an emergency, like to start the engine... they can be different size batteries. I would still recommend you use the same type/chemistry of batteries unless your charger can handle multiple voltage outputs independently-most can't.
 
#6 ·
I also have to replace my batteries and I am thinking about changing my house battery to two 6 volt golf cart batteries and keep one 12 volt starting battery. Anybody have any suggestion as to what brands are reasonably priced. My funds are limited. As well, what do you think of this setup?
 
#7 ·
Ronbye-

I have two Trojan T105 6V batteries as my house bank, but will probably add two more to make a larger house bank. It's a good way to go, and they provide a lot of power at a reasonable price. I wouldn't go cheap on the brand, since that usually ends up being a bit more expensive in the long run.
 
#9 ·
cost and size. Two T105 6VDC golf cart batteries give you a fairly decent small house bank of 210 Amp-hours when run in series for a fairly low price.
 
#10 ·
sailingdog said:
cost and size. Two T105 6VDC golf cart batteries give you a fairly decent small house bank of 210 Amp-hours when run in series for a fairly low price.
So there would be no need for a dual batterie switch? I would just need an on or of switch? What if one batterie fails? woulden't that leave me without backup?
 
#11 ·
You generally have a separate starting battery bank, which is not normally connected to the house bank. That gives you the backup. You'd still need a battery switch.

If you've seen what 12VDC batteries look like... you'd understand. A 210 Amp-hour 12VDC battery usually is an 8D battery. It weighs 130 lbs or so. It is 21" x 11" x 10". A T105 6VDC golf cart battery weighs 62 lbs. and is 10.5" x 7" x 11", and is much more manageable.

You can generally fit two or sometimes three T105 batteries in the space of an 8D. This means you can pack in more power in the same amount of space, without blowing out your back. :D
 
#13 · (Edited)
Dog,
you know I luv ya like a brother (ok, so I tolerate those twits, but you know what I mean) :) but mary, joesph and baby jesus, not everyone needs a bank big enough to power las vegas. remember what the guy said.

"OK. My boat is an S2 8.0B with an alternator and full charging capabilities. I only plan to use limited electrical, such as nav lights and radio when needed."


also he has a saildrive... so that gives him what, a 20 amp alternator?

so put your solar stik down for a minute willya? (tongue firmly in cheek)

go to pepboys, sams, wallyworld, napa, tractor supply house and grab a group 31 wet cell for less than 75.00,
(110 Ah/535 CCA) hook the darn thing up to the big red switch and go sailing!

Or, if he has a wild hair, got nutz with a 4D! (160 Ah, 800 CCA) for a hair over 120.00

yea, yea, acid spills, venting.... pfffft, if he heels that
S2 -8.0 over far enough to spill battery acid, that'll be the least of his problems.
cost justification? youbetcha, agm/chromeplatedtittleatorvalves and 400.00 bucks for a battery that will last 5-6 yrs just doesn't pass the smell test in this case. The wet cells even with heavy cycles will last 3-4 years, at least.
 
#14 ·
For a boat this size and use, a Group 27 or 31 deep-cycle is fine for the house battery. A simple On-1-2-Both switch is all thats needed to control the two batteries. Just remember not to leave the switch in "Both" when at anchor or you may not be able to start the engine in the morning!
 
#15 ·
some months ago there was a discussion on an other net or maybe this one about leaving the battery switch on "both". One guy did that & measured the actual currents between batteries for several days before charging them. His conclusion was that if all the cells of both batteries are good then the higher charged battery will NOT be drawn down by the lower charged battery. Any load will be 'shared' in proportion to their charged state. Also, that the charging currents are proportional to the state of charge of each battery.
 
#16 · (Edited)
USCGRET1990 said:
According to your measurements, two 6V batteries would take up the space of 21x14x22 @ 124 lbs. vs. an 8D that is 21x11x10 @ 130 lbs.
Altough cheaper, the two 6's would require a bit more space. Something to consider.
Ummmm... You might want to check your math. Two 6V T105 batteries take up 10.5x14x11. You're measuring for eight T-105s, not two-as you've doubled all the measurements... getting the size of two batteries, side by side, doubles only one of the measurements....

CP-

I wasn't saying the OP needed to have this much electrical battery capacity... but also was mentioning that a 75 Amp-Hour house battery is pretty small. If you're sailing for an overnight trip with the instruments and VHF on for sixteen hours or so (eight hours sailing per day) and then an anchor light for the night... you may be pushing the limits of the single 75 Amp-hour battery.
 
#17 ·
Geeze, all I wanted was another battery! HE HE ;) Just kidding. What I've done is, I ran to TRS and bought two batteries of the same size and price and compatable with the one O got from West Marine, they are identicle twins. My house system is set up for two 12V batteries, that's what the forms in the engine well are ment to be. I feal better running things on one battery for as long as needed then if I switch to another it's because I need to. Double redundancy is most favorable with as few complications as possable, K,I,S,S. Sailingdog, you've been a great help, I'm glad I talked to you. You've layed out some basics I had to know. Keep up the good work, You are appretiated!!!! Buy the way,, If I ever spill the acid of those batteries, I'm sailin' em like I got em!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top