Wiring up two batteries

S

slaydown

Active Member
Hey fellas,
Just getting the boat into the final stages of set up. Just picked up a 2007 merc 9.9 4 stroke but doesn't have the charging on it. I have done some research and I think I can get a kit for it but in the meantime I am stuck with just my main for charging. My question is now that I have my new electric downriggers Im pretty sure I need to run a two battery setup? Im just wondering how you guys would wire that up so that I can protect my starting battery and be able to charge both. Thanks for any replies.
 
Battery switch, 4 position (off, 1, 2 and combine), on post one hook up the positive from your start battery, post 2 positive from deep cycle. Common feed to the positive side of a bus bar (such as Blue Seas Dual Bus Plus). Hook all the grounds from batteries and motors to the negative side. Hook your kicker positive to the positive side of the bus bar. This allows you to select battery 2 when trolling, isolate the start battery and draw from the deep cycle to run your riggers and electronics. Select batteries one and two when running at speed on the main motor to keep both banks charging from the alternator. Get every wire with the exception of the battery cables off of your starting battery posts to ensure you don't drain it. I prefer to keep downriggers, bilge pumps and a VHF (all fused of course) wired to a bus bar fed directly by the deep cycle battery so that should anything go wrong, I can switch off all circuits on the boat, pump water, make a distress call and get my cannonballs out of the water (so they don't hang up on bottom and cause the boat to spin sideways into the current/waves).
 
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Thank you so much guys, that blue sea add a battery looks awesome especially since I don't have charging from my kicker. Now where to find one on the mainland. Thanks again
 
I have an off ,1 2, Both that you can have for postage from the Seattle area if you want to go that way. I went with the ACR because I have Radar and occasionally with the kicker running and radar on, I would start the big motor and the voltage drop would make the radar restart. The ACR has a connection from the main motor start switch that when connected eliminates the possibility of voltage drop on the house battery when starting. It also charges both batteries without having to be on the Both setting of the old switch.
 
slaydown said:
Thank you so much guys, that blue sea add a battery looks awesome especially since I don't have charging from my kicker. Now where to find one on the mainland. Thanks again
Click to expand...
Any marine place will have them or can order them in. West Marine and Steveston Marine carry them.
 
if you are using your electronics and downriggers a lot you will have to run your main a lot or your house battery will drain too far.
 
i used to use the 1 2 both switch, never had any issues draining battery #2 in a days trolling.

now i have the blue seas add a battery kit with starting and deep cycle kit and dont even think about battery charge


when​ you get the charge kit for the merc kicker just add it to the starting battery and the acr takes care of the rest
 
Google Portland Marine ELectronics, they have a great video explaining Blue Sea's ACR. totally convinced me to install the system on my Double Eagle 185
 
I had a 1,2, both switch with 2 Interstate deep cycle start batteries on my Campion and never had a problem draining the house battery with 2 downriggers, VHF, and fish finder running. I monitored the battery voltage on my Lowrance and if I saw it was getting too low would run the main for a while. I also had a deep cycle start for both batteries. I heard it is good to have matching batteries for the charging load. Rather than a regular start and then deep cycle for the house.
However the ACR is way better for a set it and forget it solution. Everyone on here likes them.
I did run an green LED to my outside and inside steering stations so I can make sure the batteries are combined and charging when either the kicker or main is running. Is real easy to do.
 
Last edited by a moderator:
Sir Reel mentioned something I've found useful too - Lowrance HDS displays (and most other brands too I would think) have an easy to set up data overlay so you can keep an eye on battery voltage any time. The difference between a fully charged battery (12.5 V) and one about to slide into 'flatbattery' territory (11.8-12.0 V) is pretty fine. Most analogue dash gauges won't have the accuracy or resolution to show this.
 
a copy and paste...

Any standard voltmeter can be used to measure battery Open Circuit Voltage (OCV). Use the following guide:

100% = 12.7V+
90% = 12.58V
80% = 12.46V
70% = 12.36V
60% = 12.28V
50% = 12.20V
 
Thanks for posting this, Coholips. Do you mind sending a picture of your installed switch? I'm thinking of ordering one for my 16' Lund with a 50HP outboard but I'm just not sure if there's enough space in my tiny battery box. Alternatively, I was going to buy a 3rd marine battery and use it as a backup on board but this switch seems to be a more feasible option at a similar cost.
 
Just ordered one also for my 16ft harbercarft. I will need to figure it out also. Will post pics when done
 
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