Blue Sea Systems Add-A-Battery Kit


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  • Simplifies switching. Isolates engine and house circuits. Combines batteries for emergency starting
  • Tin-plated copper studs for maximum conductivity and corrosion resistance
  • 12/24 Volt DC 120 Amp Automatic Charging Relay (PN 7610) automatically combines batteries during charging. Isolates batteries during engine cranking and when not charging
  • Includes E-series dual circuit plus battery switch (PN 5511E)
  • Shares the charge between two batteries more efficiently than a battery isolator


Blue Sea Systems

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The Mini add-a-battery plus simplifies switching with a dual circuit plus battery switch and allows you to charge at or away from the dock with the battery link charger. The 10A, 2 bank, charger includes an integrated 65A acr for automatic charging of 2 battery banks off a single engine alternator. The battery link charger is ip-67 waterproof and includes battery temperature compensation, start isolation, and comes with an external indicator remote. Battery temperature compensation allows you to charge a battery based on its temperature to ensure it's always receiving safe and optimal charging voltages. Start isolation ensures that sensitive electronics are not subjected to the voltage sags from engine cranking. The external indicator remote allows a customer to understand the charge status of their system at or away from the dock. By integrating switching and AC/DC charging the Mini add-a-battery plus makes boating simpler and safer. Reducing the possibility of someone being stranded with a dead battery. For use in 12V applications only.

Product details Style Name: 120A DC
  • Product Dimensions: 6 x 5 x 4 inches ; 1.5 pounds
  • Shipping Weight: 2.3 pounds (View shipping rates and policies)
  • Domestic Shipping: Currently, item can be shipped only within the U.S. and to APO/FPO addresses. For APO/FPO shipments, please check with the manufacturer regarding warranty and support issues.
  • International Shipping: This item can be shipped to select countries outside of the U.S. Learn More
  • ASIN: B000RZNP5K
  • California residents: Click here for Proposition 65 warning.
  • Item model number: 7650-BSS

After much reading and actually calling and talking to Blue Sea's tech support I'm very impressed with this product and their support. I know others have worried about the small voltage drain from the ACR unit. The ACR unit uses a small amount of current and over a VERY long time and it can drain the batteries it’s monitoring. I talked to the Blue Sea's Tech about this, and they had estimated about 4 months of just sitting there monitoring the battery voltage before the voltage drop would start to cause problems starting the engine. (This would depend of course on the condition of the battery and size/rating of it). However, when talking to the tech about this, there are a few things you can do to completely turn off the ACR. First if you hook it up like they show in the product picture you will need to hook up a small toggle switch to one of the three spade connectors on the unit to turn it off. Or if you are like me and want to KNOW everything is turned off when you put your boat away, you can wire as I have diagramed in the picture attached. By putting the ACR on the "downstream" side of the switch, you can turn everything off when you turn off the main switch. This will still allow the ACR to monitor the batteries when you have the boat in use and will function normally. The only thing would be if you put a charger on one of the batteries when in storage, you would want to leave the master switch to the “on” position so the ACR could function and allow current from one battery to the other. Otherwise, if you had the master switch in the off position you would only be charging the one battery that the charger is hooked up to. The batteries would be isolated from each other and from the ACR.

Also, when I was speaking to the tech I mentioned I was I was worried about the 120 amp rating of the unit when the ACR engages. If there is a big voltage differential between the two batteries, there would be a surge of current across the ACR when it connects the two batteries. This 120 Amp is a continuous rating and the ACR will not engage the circuit if there is too big of voltage difference. This would be a case where one battery is bad, has a bad cell or has an extremely high load on it and cannot maintain a high enough voltage. The ACR will disengage and will try to isolate the batteries in that case. In continuous operation the ACR would really only see the total amount of output that the alternator could generate. In my case this is about 100 amps so the 120 amp ACR unit is sufficient.

For the product itself, it is very solidly made, and has been working flawless. I had a Pergo basic 1, 2, 1+2, Off switch in my boat, and got tired of trying to remember to flip the switch to 1 when anchored out, then back to 1+2 when cruising around. With this no need for any of that. Just turn the main switch on when I’m getting all the stuff loaded in, and off when we put it in storage. SIMPLE SIMPLE SIMPLE.

This is an excellent kit for adding a battery to your 4x4. While it is designed for marine use, it's perfect for mounting under the hood and controlling a second battery. The smart relay is particularly clever, being able to sense a charging voltage on either side of the relay. So for instance, when it senses charge from your alternator on your #1 battery, it will close the relay and and charge the #2 battery. Similarly, if the solar system is charging the #2 battery, once it's full the relay will sense a charging voltage and close the relay and charge the #1 battery. The relay can also be turned off with the charge isolation circuit, so this is a very smart relay indeed.

The switch is actually optional, but it allows some particularly handy options. Depending on how you wire it, you can use the switch to turn off the whole system, to use both batteries independently and to electrically combine both batteries through the high current switch. Combining the batteries would allow a self jump start in the event of a dead battery, or to increase the power available when winching.

Realize with this kit you will still need appropriate wiring, fuses at the batteries, a ground bus, and several hours to install properly. You will also need some understanding of electrical circuits and how they work. There are several equally good and safe ways to install the add a battery kit. There is a recommended circuit diagram in the included instructions, and there are several other slightly different variations on Blue Sea's website. I thought both the included instructions and the website information very helpful.

In summary this is a high quality and robust kit from a high quality company. HIGHLY RECOMMENDED.

I really like this system for maintaining the two batteries on my small dual console boat. I installed the kit myself with relative ease. It seems to work as advertised. However, I have had two failures associated with the Charger/ACR. The company is fantastic and has replace the unit on the first failure. I am currently dealing with the second failure now. I have learned that the company had a massive fire and the storage facility was a complete loss. They are working to get their stock back and get me a new unit soon. I have also learned that they have changed suppliers and they have assured me that the replacement unit will have much improved reliability. I think they redesign some of the electrical components with more reliable components. I really like this system and hope to get it back together and functioning soon. I recommend this product but wait for the replacement versions to arrive. Make sure you are ordering a newer style product. I don't have any suggestions on how to do that other than checking with Blue Seas directly.

As expected from blue sea systems, a very nice item. A must have on a boat. No more worries for switching from one battery to another. A peace of mind....

Excellent quality product,well designed,with excellent instructions,only down side is that although there are the option to surface mount,or recess mount,the later option,doesn't have a template to make ease of fitting easier,although ther are very good drawings and dimensions

awsome product so far, only used the boat 3 times. followed the wiring instructions included, you need some basic wiring knowledge. lots of cable needed to connect batteries and switches. I have very limited room so it was a tight fit. very easy system to install to add a xtra battery.

Installation was a bit tricky for someone that doesn’t understand basic electrical but I had some help from someone that did understand it and after install we did some testing to insure everything worked as expected and it did and still does. Very happy with this setup now, I don’t have to worry about draining my battery too much while the engine is off.

Fairly easy to install.
You need a bushbar and extra cable. $
System is great, charges both batteries as advertised.
You dont have to worry about the starting battery dying.

Pour batterie bateau

Perfect way to simplify a 2 battery system

va etre installer dans un ponton, une baterrie de demarage et 2 bateries instrument

Loved this product if you install another battery in a boat this is the best system I found to manage both batteries

Ajout d’une batterie de démarrage

Great product

Switch is a bit bulky but otherwise great product.

Easy to install. Good instructions

Blue Sea Products are amazing. I love my VSR. GO BLUE SEA!