2nd Battery

[reelapeelin]

Originally Posted by keepitgreen05

sorry for the wires i am actually charging the right now

Thats what I did w/my '84, but turned the two batts long-ways front-to-back and all the way to the sides...that left clear access to the bilge pumps and bilge areas in general...

[tartuffe]

Dual Battery Wiring


This article describes several techniques for interconnecting outboard motors and dual batteries. There are two distinct applications: single engine installations and dual engine installations.Single Engine/Dual Battery

The use of a single engine and dual batteries is one of the most common installations found in outboard powered boats. Interconnection is straightforward. The diagram below shows the typical wiring.

Dual Battery/Single Engine Typical Schematic
NOTE: The battery positive leads are shown in red. The negative leads are shown in green for clarity; code suggests the use of yellow wire. Wiring gauge is determined by current demands and length of the run. Typically 2-AWG is used to connect to the batteries; 10-AWG is used to connect to the distribution panel. The single switch is an OFF-1-BOTH-2 switch.
JWH.

The use of a switch and wiring like this is recommend with dual battery installations. A brief explanation of the operation of the switch in this circuit follows.
In the OFF position, the two batteries are disconnected from all loads. The OFF position is used when the boat is being stored or otherwise not in use. It prevents any drain from the batteries. This can be useful if a circuit has been accidently left on, say a cabin lighting circuit or similar drain. Such a load can completely discharge a battery in a day or two, leading to an unanticipated dead battery situation when you return to your boat. On some switches a key lock is provided, allowing the switch to locked in the off position. The provides another level of security in preventing the boat from being used when left in storage or unattended.
In the 1 position, all loads and charging currents are connected to the No. 1 battery (the PORT battery in the illustration). Starting current for the engine starter motor is supplied by the PORT battery. When the engine is running, surplus current developed by its charging circuit will flowing into the PORT battery. Current to lighting and other loads will flow from the PORT battery. The STDB battery is completely isolated and has no load current, nor does it receive any charging current.
In the 2 position, all loads and charging currents are connected to the No. 2 battery (the STBD battery in the illustration). Now it supplies current required by starting and running, and it receives all the charging current from the engine. The PORT battery is totally isolated.
In the BOTH position, the two batteries are connected in parallel. This has a number of implications. Unless the batteries have exactly the same state of charge, the combined voltage to the two batteries in parallel will sag to a voltage somewhat lower than the highest battery's terminal voltage. Current from the higher voltage battery will flow into the lower voltage battery and begin charging it. As long as the state of charge in one battery is higher than the other, the lower battery is more of a load than a source of power. Eventually, the batteries will reach an equilibrium, and they will both have the same terminal voltage. At that point they will both tend to supply current to loads that are attached to them, and they will both receive charging current furnished by the engine.
It would seem like operating in the BOTH position would be beneficial, but that is not always the case. Even thought the batteries will eventually rise or fall to the same terminal voltage when connected together, they will not necessarily become exactly the same. A battery (or any source of electrical engery) can be though of as having an internal resistance. The lower this internal resistance the greater the current it can supply. The internal resistance will also affect how the battery absorbs charging current. Even though they are connected in parallel, it is possible that they will supply unequal currents to the loads, and it is also possible that they will accept unequal currents from an the engine charging source.
If the batteries are significantly different in their age, their type of construction, and their state of charge, this unequal distribution of current can be more significant. To describe the situation in the simplest of terms, when two batteries are connected in parallel, they will probably tend to behave more like the weakest battery of the two than the strongest.
Paralleling the batteries can come in handy in some situations. For example, both batteries may be discharged to a point where neither alone can provide enough current to crank the starter motor, but combined in parallel they can turn the engine over.
If one battery is fully charged and the other is totally discharged, connecting them in parallel (by using the BOTH position) can cause very high currents to flow between the batteries. Extreme heat can be generated by the sudden charging of the discharged battery. Use caution in this situation. It is better to recondition a discharged battery by slowly re-charging it with an AC-operated battery charger.
The arrangement of the contacts of the typical OFF-1-2-BOTH permits the operation of the switch in the range of 1-2-BOTH without ever disconnecting the batteries from the load or the outboard charging circuit. This is important, as it is possible to cause damage to the charging circuit if the battery is disconnected while the engine is running. By choosing the path of rotation of the switch, it is possible to change from 1 to 2 without moving through the OFF position.

[Destroyer]

Great article Tartuffe. Thanks for posting it. About the only thing I could add to it would be the recomendation to always use identical batteries in a dual battery situation. That way the drain from them and the recharging of them would be easier to manage. Not always pratical for sure, but better than having two dissimilar units.

[bgreene]

Two battery systems when properly set up are terrific and provide excellent security and back up .

I've run boats with one & two battery systems and currently run my V21 with one.
New, proper size, and plan to replace every 4 years. For many boating situations, I believe a single battery is fine.


That said, I considered a 2nd for the V, and always interested to listen to other ideas.

[macojoe]

i just put new battery's in yesterday, two 27m-xhd from interstate battery's. 850 cca, 1000 mca
Boat started right up after a long winter nap!!
switch #1 to first battery, #2 to 2nd battery, i also have a wire running to the cabin for all power to front, that comes off the 2nd battery, also a 1100 gal bilge pump to each battery.
Start boat on #1 battery then put on both to charge, then when fishing i stay on 2nd battery all day, so if i kill it i just switch #1 and start and go. but always on bth batterys to charge on way in.
has always worked for me with no issues! but agree to have same batterys for same charge and discharging.
my pumps go right to a battery, 1 on #1 battery and 1 on #2 battery with no fuse and one mounted a little higher then the other. this way one will work till first battery dies the the 2nd one will take over till that battery dies.no problem for a burned out fuse if none there.
I also have a 700 in the rear and a 500 that are hooked up with manual switch to pump anything i see before the auto 1100's do, they just for when boat is on the morring

[tartuffe]

Question guys, I have a two-battery system with dissimilar batteries, one is a starter and the other a deep cycle. I keep them in parallel most of the time but when I am bottom fishing I switch to the deep cycle. I have sat for more than 5 hours without ever having an issue with multiple items drawing power.

Are you guys with duplicate batteries running deep cycle or starting? If starting batteries, how many hours of radio/stereo/live-well pump/occasional lights time are you getting out of a battery?

I ask because I am about to go with new batteries (been 4-5 years) and would like similar batteries but question if using deep cycle for starting works. Alternate is using starting batteries for long-draw applications.

[macojoe]

i have never seen a need for a deep cycle battery, except for a trolling motor or other high use item. i have used regular battery for everything else, but nothing is of high demand.
but i also use electric reels for cod fishing and have always used a friends deep cycle for that.

so the answer for you is if you are using electric trolling motor, live well all day or electric reels, or other high demand stuff, then yes you need, but if its just everyday stuff then no

[Destroyer]

Both my downriggers are electric, so lately I've always gone with deep cycle batteries (commonly called Marine batteries). But truthfully, I've used automotive batteries many times for many years with no problems. The deep cycle batteries are really only good for applications where you really discharge the battery. (Like Downriggers, Reels and Trolling motors) Otherwise you'll do just as good with an Automotive (car) type of battery.