The dreaded second battery thread

[trentbt1]

I recently added a larger stereo system to my boat and was recommended to add a second battery for the stereo. I was directed to buy a perko switch and after purchasing a new battery I dove into the project. My original setup, single battery, engine ground to - terminal, starter to + terminal and a smaller black wire going to the negative post and a smaller red wire going to the positive post. I imagine those wires are for the accessories? Anyways, I added the second battery, wiring the starter cable to the common post on the switch and the starting battery to #1 and house battery to #2. I ran a cable in between both battery - terminals and left the ground connected to the original starting battery from the motor.

The problem is, i’m not untimely sure how to wire the rest. My stereo is currently hooked into the ignition so it only turns on when the key is moved. I wanted the second battery to run the stereo while i’m beached or tied up, but I’d also like to have it on after I start it and cruise around. What’s the best way to wire the amp and the head unit to accomplish this? I’ve tried putting the red accessory wire on the common post of the switch and leaving the smaller black cable on my battery but it only works when the starting battery is selected or when the switch is on both, the stereo
will not turn on at position 2(house battery). If i ran a ground from battery to battery, wouldn’t the smaller black wire still be grounded to both batteries even if it’s connected to just 1? Sorry for the long post, just trying to give you all an idea of what i’m doing wrong! Thanks!

 

[alldodge]

First you have to disconnect the stereo and amp from Bat 1 (Start)and the key switch. Those items need to be connected from a feed coming from Bat 2 (House). While you can use the same ground, it is best to add additional ground wire up to the amp and stereo.

Have both Bats connected together with heavy ground cables attached to the block.

Add a buss bar and/or another fuse panel for the stereo and amp unless you use inline fueses, then it will be acceptable to just use a buss bar.

Adding an ACR for automatic charging when motor is started would be best

 

[Lowlysubaruguy]

Here’s how I run my battery isolation switch which has four positions 1 2 both or off #1 is use for engine starting tasks or both of they are both charged and when running I switch to both 1 & 2 so all are charged. When sitting I use #2 if it’s drained that battery #1 will still start it. Some recommend not switching when inoperation but I have done this regularly for 20 plus years just do it quickly without hesitation. Grounds are hooked up constant battery positive is what’s switched.

When i I leave the boat I turn the blower on and then turn the battery switch to off I hear the blower shut down and know both are disconnected I loose radio memory but that isn’t a concern for me, this is all different if your moored or charging from a non engine powered charger. You’ll need to have one battery live for bilge or both if your hooked to power for charging.