I'm pretty anal about keeping up with my boat maintenance but last week I got caught. I had been thinking one of my two boat batteries was not in good shape and likely needed replacing. Usually if I hadn't used my boat for about a month I would put my trickle charger on the batteries (battery switch in BOTH position). Didn't this time. Headed out to fish Entrance Island and the waterfall. Beautiful afternoon. Dropped the lines and within 1/2 hr of working them realized the battery switch was in the BOTH position and both batteries were dead. Limped back into boat ramp on trolling motor (actually it was a nice ride). My question is this: what is the best way to run two batteries. I believe my downriggers are wired directly to #2 Battery and my other electrical equipment is wired directly to #1 Battery. I have been thinking the battery switch is really just switching which battery I will start my big motor with. I have also been thinking that I should run on #1 or #2 Battery positions when fishing and only move to BOTH when actually running the big motor to charge each of the batteries. How do the rest of you operate with two batteries?
DD

Hey John, on my last boat I had all my electronics on # 2 and used # 1 just for starting the main engine. I had my downriggers on # 2 as well. Always wanted to know that I would not drain the # 1 battery and when running I would have the switch to both.
I never had any problems.

Knota-Kanu

From what I've read, technically you only ever want your switch to 1 or 2 unless you're having trouble starting and need extra juice.

The whole point of having the switch to have redundancy, running it on both will defeat the purpose. Plus a bad battery will zap a good one in no time

I agree with what you are saying basically. Just wondering though...if you were going to run out to your favorite fishing hole 30 minutes away...after your motor was started - if you switched to the BOTH position - would the motor's alternator top up both batteries while running out to our spot?
When I fish off the West Coast for a week - we do not have electricity available although I do have a generator and a trickle charger and a solar panel. After a few days of fishing running the downriggers up and down - I need to recharge their source battery.
DD

ya I hear you, I have my share of battery related issues on boats. I will say I'm not an expert on all things electrical but I think you are better charging one battery at a time. Running on both I'm not sure you'll ever get a really good charge and I'd rather have one fully charged battery then 2 batteries at 60%.

Maye someone with some more know how will jump in?

I think you are best to charge one at a time. Maximize the charge to one battery at a time so you do not dilute the charge should you only have one good battery. I usually run out on #1 and then switch to #2 when fishing. My kicker charges #2 tho so I am usually good to go.

Thank you RBF. I understand what you have said. When I am able to replace my kicker I will purchase a four stroke with charging system for the batteries. In the meantime I have to be careful that I don't kill both batteries especially when I get off the west coast.
DD

Hey DD,

You may be able to get a charging add-on for your current kicker, that might be something to look in to?

Scotty downriggers, with a 15 pound ball attached, draws 8 Amps (with your main engine running) = 13.8 Volts, 8 Amps, 1.725 Ohms, using 110.4 Watts. Now turn the engine off and this is what it looks like = 12.6 Volts, 8.7619 Amps, 1.43804 Ohms. That is figured using the 110.4 Watts. Multiply that X 2 downriggers = 17.5328 Amps usage per hour. If your selector switch is in the both position, you WILL drain both batteries, even if trolling with your main. I doubt if your main will charge 17 Amps per hour at an idle. How much you actually will drain the batteries depends on the use of the downriggers!

But, if the downriggers are used for 30 minutes out of each hour, for 10 hours trolling there will be a discharge of approximately 58 Amps. This is NOT the state of the battery, it is the amount of Amps used. Now, run in and out with the main engine/engines, so no problem the engine will charge the battery/batteries. Figure if your alternator produces 40 amps and you run for 30 minutes, best case that will give you 18.8 Amps going back to the charge the batteries. Now if you have the switch in both, that would be 2 batteries getting the charge, that is 9.4 Amps, each? It is just a matter of time the batteries will be discharged to the point, they will not be able to start your main!

You really need to be turning that selector switch to either #1 or #2 and I don't care what anyone tells you, never run yours on both! It is also true if in the both position the batteries will equalize, actually discharging your fully charged battery, as it tries to charge the other, not good! You can wire the downriggers and electronics to your battery selector switch or to battery bus. That way you can select either battery and have everything running off the selected battery?
If you leave them wired to #2, change everything to run off #2. Just keep #1 as a backup, which is basically what I do. I have twins, so one engine charges one battery and the other charges the other, so I always have a good battery for starting. Just so you know, it takes about 3 days fishing before my #2 will not start my main, but I run a LOT of crap off my #2 battery.

But, if you run the battery switch in "both", a portable battery pack or spare battery would be highly recommended, as you will be needing it!

I used to have the battery switch option on my old boat.Got caught once out on the west coast with both batteries dead because one sucked the other down.Good thing it was a yank start kicker.On my boat(old boat) I changed to one battery dedicated for main engine start and one dedicated for electronics (charged by kicker).I have the wing nut connections on the battery so I can manually swap them if trouble arises.(Haven't swapped the new boat to this yet).I just found for me it was better that way.Also read some place about blowing diodes in your alternator if you switched the battery switch while running,maybe on the battery switch instructions?Also how many of you guys have jumper cables in the boat,cheap insurance.Dan