Blue Sea Systems 7650 Add-A-Battery Kit - Dual Circuit Battery Management System, 120 Amps

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.

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.

I kept having problems once I switched this no problems occurred at all. It is really awesome piece of equipment.

I purchased my 2004 Boston Whaler center console back in 2005. It has a twin battery set up and came equipped with the traditional Perko abttery switch that has the 1 / 2 / All switch positions. I use my boat for offshore fishing trips so having enough battery power available at all times is paramount. Over the last couple of years I've noticed that the boat wouldn't start off of battery one. And on a couple of trips, it wouldn't start off of battery two. This got me thinking that one day, I am going to be left stranded with no battery power. Since those instance, I have started to carry a portable jump starter, however, I wanted to see if I could get an additional layer of safety built it. One of the things I really hate about the traditional battery switch is that you have to remember where you left the switch positioned. You may switch it to ALL to get the boat started and even cruise with it in ALL to make sure both batteries are charged for when you anchor up at your fishing spot. BUT, if you forget to switch it back to 1 or 2 when you get to the spot and you start dropping lines, listening to your music, running your bait wells, fish finder, etc, you could end up draining both batteries. This is where this Blue Sea Systems kit comes in.The installation was relatively simple. I did it myself in a few hours. The logic behind the system is elegant and simple. There are two main positions: On / Off. When you want to use your boat, turn the switch to ON. When you're done, turn it OFF. There is a third position (combine), but I've never had to use it.How it works: The kit monitors voltage in your batteries. When the voltage in your battery drops below the threshold for starting the engine, it cuts off flow from that battery- isolating it. When charging, the kit bridges the two batteries so they both charge. It's simple, elegant and most of all, safe.