One battery or two

valleydawg

Seaman Apprentice
Joined
Nov 10, 2009
Messages
46
My new boat (used 05 23 ft CC) has one battery. I like the idea of two. Should I use both or have a switch for the second one or leave it unhooked (but charged). Not sure how most do it. Thanks
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Re: One battery or two

Switched. Gives you the option to use #1, #2, or both.
 

redone4x4

Lieutenant Commander
Joined
Feb 28, 2009
Messages
1,548
Re: One battery or two

i leave mine unhooked but charged. if we are out for more than a day i manually switch the cables over to the other battery. its just 2 wingnuts. I might do the battery switch in the future but for now this works great.
 

Mike Robinson

Senior Chief Petty Officer
Joined
Jun 29, 2005
Messages
752
Re: One battery or two

Another alternative is to get one of the power packs that have jumper cables built in so you can jump your battery (or somebody elses) if needed.
 

ovrrdrive

Petty Officer 1st Class
Joined
Apr 28, 2008
Messages
265
Re: One battery or two

I have 4. One starting battery, two for the trolling motor and a "house" battery for the radio and electronics. I just got a 3 bank mounted charger for the 3 in the console.

If I were to get stranded I could manually move a fresh battery to the back of the boat to crank the motor.
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

The best setup I've found for dual batteries (single engine) is a switch and an ACR (Automatic Charging Relay). The ACR keeps both batteries at full charge all the time. You never touch the switch unless you kill your primary battery or it goes bad. The second battery is not used (unless the bilge pump connected to it is running!) until you need it.

The ACR also lets you know the status of your batteries and alternator so you're less likely to get stuck out on the water! It has a connection for a remote LED that glows if both batteries are charging OK, or blinks if you have a bad secondary battery (won't come up above 12.35 volts). If it stays off with the engine running it means that the primary battery voltage is low. It will stay off for about 10-15 seconds after you crank the boat because the starter pulls the battery voltage down, and it takes a few seconds for the alternator to bring it back up. But if it doesn't light up after a few seconds then either your primary battery is going bad or the alternator isn't charging. It's a great way to keep track of the status of your batteries and charging system.

http://bluesea.com/products/7610

Mine is wired as shown below, with two independent bilge pumps (also wired to a common switch on the dash) and a green LED from the ACR on the dash. It's a nice feeling to see that LED glowing anytime the engine is running and know that both batteries are charged and good.

CrownlineBatteryWiring7-10.jpg
 

JoLin

Vice Admiral
Joined
Aug 18, 2007
Messages
5,146
Re: One battery or two

45Auto- Excellent schematic- couldn't be any easier to follow. I have 2 batteries on a switch and have thought for awhile about adding an ACR.

I right-clicked and saved it to my PC. Thanks!
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

Thanks John. I had to make it a few years ago just to keep track of all those wires in the battery compartment!

If you already have a switch, the ACR just wires in between the terminals on your existing switch. Make sure you use heavy tinned MARINE cables because they'll be carrying your full alternator output. Automotive ones are MUCH cheaper, but corrode and lose continuity after a couple of years - that's why I had to make the diagram above, so I could troubleshoot the system when my little LED wasn't glowing after it's second year. Turned out to be all of the oxidized automotive cables I had used originally because I was cheap!

Either do it right the first time, or it'll bite you later (like I've never heard that before ......)!
 

98sanger

Cadet
Joined
May 26, 2009
Messages
10
Re: One battery or two

45 Auto -

This looks like the setup I want. I want to crank the boat on BATT 1, cruise in 1+2 and play the stereo off BATT 2 only. Should I wire all power from the stereo equipment to BATT 2 directly? Or should I just put it on the common lug on the switch?
 

Beefer

Lieutenant Commander
Joined
Aug 4, 2008
Messages
1,737
Re: One battery or two

For the $$$, it seems like a steal! So, forgive me, but if I understand correctly, it charges both batteries while underway or the engine is running, but it does not charge them when the boat is not in use. Is that correct?
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

This looks like the setup I want. I want to crank the boat on BATT 1, cruise in 1+2 and play the stereo off BATT 2 only. Should I wire all power from the stereo equipment to BATT 2 directly? Or should I just put it on the common lug on the switch?

You don't have to touch the switch. When you are cruising the ACR automatically combines #1 and #2 to keep both of them topped off. The LED on the ACR (or the remote LED if you hook it up) will either blink if #2 won't charge or not come on at all if #1 won't charge.

I put all my accessories on the common lug on the switch. Only time you'll need to move the switch is if #1 goes bad, which will probably be once every 5 or 6 years.

If you have a big enough stereo to drain a battery in a day, I would wire the stereo straight to #2 like you said and put everything else on the common lug. With the switch in the #1 position that would keep #1 isolated for starting, charge both while you're running, and run the stereo only off #2.

I also have a bilge pump with an auto switch wired straight to #1 and a totally separate bilge pump with auto switch wired straight to #2.
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

For the $$$, it seems like a steal! So, forgive me, but if I understand correctly, it charges both batteries while underway or the engine is running, but it does not charge them when the boat is not in use. Is that correct?

That's correct. The ACR charges them both off the engine alternator while underway. If one of them won't accept a charge it keeps it disconnected so the bad one can't pull the good battery down. It's easily one of the best $100 I've spent on my boat.
 

98sanger

Cadet
Joined
May 26, 2009
Messages
10
Re: One battery or two

Excellent! Thank you so much for the reply, the thread was a bit old. I'm gonna buy the stand alone ACR and wire it into my existing setup. All stereo equipment will go to BATT 2.

So if I throw in the ACR I should start the day in BOTH and then just do whatever, when the engine is off and only the stereo is needed I swap to BATT 2. There is no real need to go to BATT 1 unless you have battery fails. BOTH and BATT 2, sounds exactly like what I want.

I guess my last quesiton would be. When you start and cruise, what are your battery settings? I understand leaving it be as it charges both BATTs as you are operating.
 

scutly

Petty Officer 1st Class
Joined
Aug 20, 2009
Messages
368
Re: One battery or two

you take the whole ACR setup one step further by installing the Blue Sea add-a-battery kit that comes with the simple on off switch. it isolates the starter and house batteries. get on the boat and turn it on then get off the boat and turn it off. no need to be switching batteries ever except in a emergency to combine both batteries. it knows what battery to use when you go to start the engine and knows what battery to switch to when the engines off but your running electronics. it also knows which batteries to charge. availabe right here on iboats.

bluesea.jpg
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

it knows what battery to use when you go to start the engine and knows what battery to switch to when the engines off but your running electronics.

It doesn't "know" anything. It doesn't do any switching between batteries whether you're starting the engine or running electronics. All it does is automatically combine both batteries when the alternator output is higher than the battery voltage.

If you wire your boat as the Add-A-Battery kit suggests then you wire all your accessory loads to one battery and your starter to the other. The ACR automatically combines and charges both batteries when the motor is running. The "combine" position on the switch ties the #2 battery into the starting circuit if you need it. Won't do you any good if the #1 battery is shorted since it will still be in the circuit pulling down all the juice.

I didn't like the Add-A-Battery kit because the switch doesn't give you the option to get battery #1 completely out of the starting circuit if it craps out. Only option you have with the switch included in the Add-A-Battery kit is to combine batteries. There's no option for battery #2 only. A shorted battery in the circuit will easily pull the other battery down too far for it to start the boat. The set-up I used is the exact same except that it allows you to take #1 completely out of the circuit.

I used the Blue Sea switch below (along with the 7610 ACR - same as in the kit) which has options for battery #1, battery #2, or both batteries:

9001e_182x182.jpg
 

thewiles

Cadet
Joined
Jul 13, 2010
Messages
15
Re: One battery or two

just wanted to say thanks to 45auto! This has been one of the most useful threads I have found. I went from knowing nothing about how to add a second battery to my boat, to an expert.
Big props for sharing your knowledge!
thanks
j
 

Home Cookin'

Fleet Admiral
Joined
May 26, 2009
Messages
9,715
Re: One battery or two

I especially like the idea of 2 bilge pumps, each wired to its own battery. Note that the bilge pumps are not fed through the switch and are "always on."

But does this rig allow you to shut off both batteries? I think that is crucial in mooring boats especially in salt water to stop electrolysis and the inevitable electrical "leaks."

I have the basic 2 battery set up, and although I can run "both" I never do, as I was told that they do not charge evenly, or "pour-over" when one is fully charged, absent a specialized switch for this. I just alternate--use 1 going out and 2 coming home, or 1 on one day and 2 on the other (remember odd/even license plates for buying gas?).

I have recently had my low batt alarm come on my GPS when there is plenty of cranking power in the battery; I guess it's set high for safety reasons. I don't run much off the battery: vhs and gps, occassional live well/wash down pump, the latter triggers the alarm. The heat must be getting to the batteries.
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: One battery or two

Either way will disconnect everything except items wired directly to the batteries (such as bilge pumps) when the switch is "off".

The switch that comes with the Add-A-Battery switch gives you the options below. There's no way to connect only the battery on the top left to the starter:


BS5511.jpg




The 4-way switch that I used gives you more options if one battery goes bad out on the water:


BS9902.jpg



With the ACR wired between the batteries, either one will keep both batteries fully charged all the time without having to touch the switch.
 

scutly

Petty Officer 1st Class
Joined
Aug 20, 2009
Messages
368
Re: One battery or two

It doesn't "know" anything. It doesn't do any switching between batteries whether you're starting the engine or running electronics. All it does is automatically combine both batteries when the alternator output is higher than the battery voltage.

ummm. i dont think that's correct

"TWO BATTERY BANKS, WITH THE ADD A BATTERY Dual Circuit System
An ideal way to switch and manage charge of the batteries while underway is with the ADD A BATTERY from Blue Sea Systems. This includes the Dual Circuit Plus battery switch and the 120 Ampere Stater Isolation-Series Automatic Charging Relay (ACR). Together, these components simplify switching and automate charge sharing. In addition, the start isolation feature of the ACR protects sensitive electronics from potentially damaging voltage fluctuations during engine cranking. The SI ACR fully automates charging of two batteries from a single charge source, eliminating the complication of ?sharing the charge? manually with the selector switch. If the SI ACR senses that a charge is present on either battery (indicated by a high enough voltage) it will offer the charge to both batteries. If the battery voltage subsequently drops to a preset threshold, the ACR will isolate the batteries. Even if the house battery becomes fully discharged, the starting battery will remain charged. The ACR will automatically disconnect when the starting circuit is engaged. Enabling this feature to isolate the start circuit from the house circuits and prevent starting currents from flowing through the ACR or starting current transients from interfering with loads on other batteries. The reaction time of the ACR is fast enough to disconnect the battery banks before the starting current rises in the starting circuit."

*Starting Isolation Features
? Automatically combines batteries during charging, isolates batteries when discharging and when not charging and when cranking and starting engines
? Allows temporary isolation of house loads from engine circuit during engine cranking to protect sensitive electronics
? Supports high-output alternators up to 120 Amps
? Ignition protected?safe for installation aboard gasoline powered boats
? Under voltage lockout?will not close when the lower battery is below 10.8V at 12V operation or 21.6V at 24V operation
? Built in LED light indicates when batteries are combined
? Meets external ignition protection requirements
? Waterproof rated IP67?temporary immersion for 30 minutes
? Designed for 12 or 24 volt systems
? Senses charge source on either battery bank

e-Series, Dual Circuit Plus Battery Switch
? Switches two battery banks simultaneously with one simple ON/OFF switch while maintaining battery bank isolation, minimizing the risk of a dead starter battery
? The COMBINE BATTERIES function offers the ability to combine two battery banks in the event of a low battery.

OPERATING THE ADD A BATTERY Dual Circuit System

Operation of the ADD A BATTERY system is as simple as using an ON/OFF switch. Upon arriving at the boat, turn the switch ON. When the day?s boating activities are over, turn the switch OFF. Setting the switch to COMBINE BATTERIES will enable paralleling of the batteries for emergency starting if the starting battery should somehow become drained or is no longer accepting charge. This enables the starting circuit to use the house battery. It is not recommended that the COMBINE BATTERIES position be employed to use the starting battery to provide additional power for house loads, or while the engine is off.

Installing the Blue Sea Systems ADD A BATTERY Dual Circuit System may prevent a dangerous dead battery situation or eliminate the need for an embarrassing request for assistance to another boater. Whether the ADD A BATTERY is used to replace a selector switch or upgrade to a two-battery system, it combines the benefits of simple operation and sophisticated technology to offer today?s boat owner convenience and peace of mind.
 
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