Name:	sagetek1 -	Reply
Subject:	Dual battery use question
Date:	2/21/2020 12:24:16 AM

This seems to be a question for the ages, but recently installed identical regular marine batteries (not deep cycle) in my pontoon boat. Marina did this an put a simple 1-2 both switch on this. No special battery sensing switches or relay, etc. Question is , wha it the best way to operate these? Did this so that when pulling up to a sandy area on lake, can run radio, etc. without as has happened, run the single battery I had then low and had to get a jump to restart.

Anyway, what I am doing now, is when starting the engine for the first trip of the day (just a 70 HP) I run on both batteries. If we stop as indicated, based on the odd or even day of the month, put the switch on 1 or 2 battery. When leaving, I keep the current battery setting and assuming the engine starts (it really should), I run the rest of the day on this selected battery.

Putting the boat up, I turn off the switch. Next trip, start the process over. Theory is that the battery not selected after pulling up on sandy area, remains fully charged and should be fresh, and the battery used last coming back to marina should be fully charged.

Anyone have any other ideas on this, or is this the best you can do without sophisticated battery management systems.

Again, batteries are identical, both installed at same time, and check volt meter routinely to see if all looks correct/same on charging voltage coming and going for the day. So far, it has. Never had one die yet. Problem single battery was old, so put in this system a year ago. Plus I carry a jump box also. learned my lesson.

Thanks!

Name:	wix -	Reply
Subject:	Dual battery use question
Date:	2/21/2020 8:28:57 PM

If it works for you....it works.   Be careful using “both” since the batteries will equalize if left connected to each other, which will cause the weakest battery to drain the best battery, which may leave you jumping off, or swimming.  I use a trickle charger and charge up the battery not used for last trip just to be sure!

Name:	sagetek1 -	Reply
Subject:	Dual battery use question
Date:	2/21/2020 8:52:18 PM

Thanks...

The only time both are hooked together is when starting for the day and running the engine while cruising. When stopped for several hours at say a sandy area, use only one and leave it as the only connected battery (assuming boat starts) till back at the marina. Then I cut it off and they have to switch back on if they need to move the boat to fork lift. Supposedly they cut off battery switch completely before putting back into storage area. Their policy and required me to have a cut off switch. Hopefully no two batteries are connected at the same time that radio, etc. is on without engine running (except when starting for first time of the day).

Name:	Shortbus -	Reply
Subject:	Dual battery use question
Date:	2/24/2020 11:27:35 PM (updated 2/24/2020 11:31:12 PM)

Run the stereo on your weakest battery. Start on your best battery, run the boat on both batteries.

I use a continuous duty solenoid that connects the battery's positive posts for start/run/charge and disconnects the stereo battery from the boat battery when motor is off.   No switching, no thinking.

Name:	F1Fan -	Reply
Subject:	Dual battery use question
Date:	2/25/2020 11:27:41 AM

We have dual batteries on a 1-BOTH-2-OFF switch. Other than the time we realized one was weaker than other and needed replacing have run boat on BOTH setting with good results. A few times when we've been anchored for an extended time with stereo on, lights, etc. have swapped over to just one of them as insurance that if we ran one down, we'd still have a second to get home.

I believe the one thing you have to be very careful of is never to swap from one to the other via an "OFF" setting in between with the boat running. I think this risks damaging the alternator if I'm not mistaken. 

Name:	sagetek1 -	Reply
Subject:	Dual battery use question
Date:	2/25/2020 1:27:00 PM

Pretty much what I do. The switch is "supposed" to be a make-before-break switch but like you, I NEVER switch batteries when the motor is running. Do not know if modern alternators could take the open circuit situation, but do not want to chance it. I too have for years heard the alternator damage question, and at one time there was even a device to put on large alternators like on Mercruiser boats (had one years ago in a large 24 foot cruiser at the gulf) to prevent this damage. Ran dual batteries there, but one was for starting and one for house. Could be paralleled if needed. Had sophisticated charging system to keep both charged even though mismatched. The ones I have now are the same.

Name:	Pontoonfisher -	Reply
Subject:	Dual battery use question
Date:	2/28/2020 8:29:19 AM

Your 70HP outboard does not have enough auxiliary capacity to keep your batteries fully charged especially if your running the radio and other devices while running.   You would probably need to run the boat for 10 hours to fully charge both batteries that are at half of their capacity.   You need to be leaving the dock with fully charged batteries from an on board charger.  

Also, best practice is to only use the both position in emergencies.  Running in the both position can hide a battery issue   

Name:	John C -	Reply
Subject:	lithium batteries for the boat
Date:	5/11/2020 7:41:15 PM

Not really an answer to your question but here's an interesting podcast I heard on a fishing guide in FL that switched to all lithium battteries. They discuss the differences in lead acid, agm, and lithium batteries. How to charge them, how to handle them, how they work differently. Here is the link on stitcher but I found it on Apple:

https://www.stitcher.com/podcast/tom-rowland-podcast/e/67455039

Name:	MartiniMan -	Reply
Subject:	Made me look.....
Date:	6/1/2020 5:02:30 PM

So a comparable lithium battery for my boat is around $2,000 with another $850 for a charger.  Yikes!  I can buy a lot of batteries for that kind of coin.  I'm sure they're great but not sure they are worth the cost.  I put a $120 battery in my boat every 3 years or so.  One lithium battery with charger costs the same as 23 regular batteries or about 60 years of boat use.  That makes no logical sense unless there are cheaper versions than the ones I found.

Name:	GoneFishin -	Reply
Subject:	Made me look.....
Date:	6/1/2020 7:59:00 PM

https://www.bigtimebattery.com/store/Deep-Cycle-Lithium-Iron-Marine-Battery-Group-34-LiFeP04-800CCA.html

$555 and weighs just 13 lbs.

Name:	MartiniMan -	Reply
Subject:	Better....but not good enough......
Date:	6/4/2020 12:59:06 PM (updated 6/4/2020 1:00:39 PM)

That's a little more reasonable but my current battery has 1,100 cold AMP cranking power.  A comparable Bansee lithium is almost $1,100 which is a measely 8 times more expensive and last only three times as long as an ordinary one.  And you still have to buy a lithium battery charger.  So it still doesn't make economic sense for a recreational boater IMO.

Name:	John C -	Reply
Subject:	Better....but not good enough......
Date:	6/11/2020 3:04:23 PM

I see what you mean right now. I do think in the future we are going to see price improvement on lithium batteries. There is a lot of research and development going on in the car industry that I think will bleed over.

Name:	wix -	Reply
Subject:	Why lithium?
Date:	6/11/2020 9:36:35 PM

I’ve got an eight year old Wally World marine battery in my boat that still works as it should.  Key to the life of a battery is to keep it charged 24/7.   I use a low amp trickle charger that holds battery at 100%, but doesn’t overcharge.  BTW, I use two batteries in all boats. No, not in SeaDoos!

Name:	John C -	Reply
Subject:	Why lithium?
Date:	7/6/2020 4:57:51 PM

the podcast I linked above is way more detailed but a few of the benefits they mentioned for boats are:

1.)    variety of how / where you can install your batteries. Lithiums are way more flexible since they don't have the water cells with caps. Old style batteries must be kept upright 

2.)    much faster charging 

3.)    no need to trickle charge. You can charge it up 100% before you leave for the weekend and then you can unplug it. You don't have to keep the battery plugged up to the charger that is connected to AC. Therefore smaller chance of a battery or charger over heating. Less chance of a a spark in an area (a boat house) that is probably enclosed and probably has gas fumes or at least gas stored nearby. 

4.)    better performance - the podcast goes in to way more detail and most of it is way over my head. But they gave a lot of practical examples, especially for fishing boats that use batteries for trolling motors, power poles, etc.