Running 2 starting batteries in parallel

I get how to put the batteries in parallel. I'm more curious how you hook all the accessories up?. Do you hook everything up to one battery as normal? Or do you hook up to positive on one battery and neg on other? How do you hook motor and charger up?

Just hook up to one battery as normal.

Does your charger charge the second battery when hooked up normal to one battery?

Yes

This is how I run mine... Its redundant and pointlessly excessive on my rig, but it came that was and I don't see any reason to ditch battery #2... Though I suppose when I had to replace them I could've gone down to one and saved money and also weight but there is also an extra battery in my TM battery compartment... So 5 total...

Spare battery life is never a bad thing though I suppose, and she has 2 bank chargers on each side to juice them up all the same... Then again I'd probably pick up 3mph if I dropped 2 batteries worth of dead weight right off the transom I bet!

It alsp shouldnt matter where you hook up, power side is power side and ground is ground, if you have enough extra comnectors at battery to justify it... But at that point you should be seeking a more elegant control circuit setup than running everything directly to batteries I reckon.

I had a couple people on here tell me not to do this...that it would mess things up.

I went ahead and put an extra battery in the boat next to my cranking battery. I wired it to my cranking battery must like you would if you were putting jumper cables on it (pos to pos/neg to neg (parallel)). It's been like this for about 6 months now and I've had zero problems. I do not have a battery charger hooked to the additional battery. It simply charges through from my starting battery when it's plugged into the charger.

As far as how I everything run....I have everything in the boat except the TM running off the one cranking battery which is backed up by the battery I added.

And, running batteries in parallel, you get more bang for your buck, so to speak.

For anyone wanting to get a bit more into the science/math behind batteries, this man's series is worth watching.

This one in particular about the extra oomph of two batteries in parallel:


Batteries in Parallel configuration

Brad

Two batteries connected together in parallel (pos to pos and neg to neg) will give you 12 volts but you have the juice of two batteries instead of just 1 so that will give you a longer run time on 12 volts. Just come off one battery to go to the + and - of your accessories if that is easiest to do. Since they are connected in parallel it doesn't matter which + or - post you come off of.

I was always told that you had to hook up to one post of each battery to get the benefits of that setup. So positive of one battery and negative of the other on all things that are hooked up.

hum might do this.

Whatever is the easiest way for you to hook them up is the way to go. It makes no difference if you come off both posts of one battery or one post of each battery. Google "connecting two batteries in parallel" and you will see pics. of it done both ways.

You have to when the batteries are connected in series.

Check out every diesel pickup truck on the market. Everyone of mine has come with dual battery hooked up in Parallel. They are going for the extra "oomph" mentioned above to rapidly turn over a very high compression motor. The second battery is simply hooked positive-to-positive and negative-to-negative. The starter, all accessories and the alternator are hooked to one single battery. Though they are identical batteries I call this the "main battery". The secondary battery is simply like a "jumper" battery off to the side. Even with everything run off one and only a positive and negative jumped over to the main battery from the "secondary" battery they both lasted 7 years on my current Dodge Cummins. This is the set up I would reccommend for your application although I think it's overkill to haul around the extra 50lbs in your bilge area. I would also question wether or not your batteries will be maintained in at a proper charge when stored unless you have them hooked to different banks on a multi-bank automatic battery charger(even more added weight). 361v

Just out of curiosity as to why you are running 2 starting batteries? Do you have that many accessories that you are afraid of not having enough juice to start after fishing all day?
I've been kind of worried about all the new electronics I've put on the boat and if it would drain the crank battery too fast. Mine is a crank/deep cycle so hopefully not but I don't ever want to find out.

Big agm group 34 or 31,would provide enough juice for everything you need on a bass boat. Running 2 in parallel is overkill, imo. I can see the potential benefits, but the you are adding 60-70 extra pounds back there. Every 50 pounds equates 2-3mph loss on top end. Not important to some, but just an FYI for you .

I would treat the second battery as a spare and use the spare battery gadget used on UTV's that allow it to charge when the engine is running, but will not discharge with the main battery. That way you actually have a spare battery on board. If main dies, switch to 'main' position and the engine will turn over using the spare, plus you can connect the big spotlight to the spare and it will not run down the main, and then charge back up when the engine is cranked.

OR, you could carry a pair of jumper cables...

Running three graphs, live well pumps, occasional talon up and down,start and stop,bilge pump, I run a 31 odyssey, absolutely no problems so far,(2 years)

About batteries -

In Parallel - Voltage stays the same, current doubles with two batteries and triples with three, and so on... (Hooks up red to red, black to black)

In Series - Current stays the same, voltage doubles with two batteries and triples with three, and so on... (hooks up red to black to red to black)

Can't remember where I heard/read it, but something about having 2 in straight parallel (vs. 2 with perko style battery switch) may cause engine alternator issues. Don't know the electric theory, but you may want to research this topic.

Hmmm, I can't see it. That's exactly how my batteries are hooked up in my F250. Now, my truck has a bigger alternator to compensate, but that' about charge rate. The change I can see is double the time to recharge them if both dead. Much smarter to use the switch in any case.

OR, the jumper cables...

I've actually started having issues with my cranking battery. Had a few trips recently where it wouldn't turn over the motor after about 1/2 day hard use. It is a 2 year old Interstate (whatever their top of the line battery is). I took it to interstate last week and it tested good. They suggested it could be my alternator or my charger, which it doesn't seem to be. I ordered a new Optima, so we will see how that works out. After the first trouble, I started trying to manage my battery better by shutting some things off when not in use and adjusting the timer on my aerator, but that didn't help. I have purchased a small jump pack to keep on the boat, and it has successfully started my 250 SHO 3 times now without re-charging. I will keep one in the boat from now on.

What is battery voltage with and without motor running? I have had a couple of Interstates through the years that were self discharging. They made good and changed them out for me.

I had battery problems with the engine not cranking over on a second day of use w/ all electrics on the "starting" battery and not enough running around time to help recharge it. Put in a second "starting" battery for the just in case scenario and a duel charger hooked to both, but had problems with graphs not working properly. Unhooked the 2 bank charger from the 2nd battery and things went back to normal. Still keep the 2nd battery in the boat but started to recharge the first starting battery after each trip and no longer any problems.

Someone mentioned the one concern I had. Can anyone speak to the increased work required of the alternator? Would two batteries cause your alternator to die sooner?

The difference between the two ways you hook up the batteries in parallel is in what are you trying to accomplish. Connecting the wiring as you would jump cables (1)will give you longer 12vdc before you drop off(Reserve Amps) and connecting them Positive Battery 1 and Negative Battery 2 (2) will give you higher starting Torque (Cranking Amps). The difference is the restriction of the wire used to connect the batteries. The wire creates a resistance during high amp current usage so (1) you will not get the same effective level of cranking amps as you would get wired like 2. This resistance can be minimize by using at least a 1/0 wire as the jumpers. My 250 merc says it requires a 1000 amp battery. There are very few 1000amp batteries out there. Putting 2 in parallel will give you this (but does add weight)

The additional draw on the alternators is minimal. Since you don't draw down two batteries as much as one the effect is basically the same.

You should use big welding cables to wire batteries together, or you will suffer loss because of too small wires.

and about two batteries and alternator load...

as mentioned, it is about the load, not the battery capacity. If the load remains the same, half comes from each battery and the alternator doesn't know the difference (if you use big connecting cables). Now, if you doubled your load, you would want to look into a larger alternator to get the battery pack charged quickly. The original alternator would not overload itself and die, it is regulated to a max current, but it will run at max for a little longer before it starts regulating the current downward, and it will take longer to recharge the drained batteries.

Thanks I have an 27xhd interstate new in the boat and I'm taking a less than 1 year old Walmart ever start maxx 29dc that I didn't want to waste so I'll get some of the welding wire and hook them up!

No. Watch that series of videos, beginning with the one I linked to above, and what you will learn is two batteries in parallel yield MORE than twice the functional current (amp-hours) of a single battery.

It makes sense once you watch his demonstration.

Brad

That's good to know. The battery tests at 12.8V. While running i am showing a little better than 14V. When i took the battery in it had been off the charger for about 24 hours. They said that everything tested optimal. The battery is still under warranty. I may take it to a retailer when it is lower and just try to swap it out.

Hooking Batteries in Parallel

This link describes the reasons for hooking negative and positive on separate batteries.

https://www.youtube.com/watch?v=bfvLcTxgvzo

Ive had 2 cranking batteries wired parallel for about 4 years now and never had a problem with low voltage since. Just ran pretty heavy cable to pos and heavy cable to negative.

http://www.tuffskinz.net/?page_id=1705



This ought to fix everyone's problems!

I stand corrected.. I didn't think about the voltage drop linking the two batteries together so it will make a difference in how you hook them up.

In place of running two batteries, bite the bullet and get an Odessy 31M-PC2150, $450-$500. CCA 1150, Reserve 205, short circuit current 5000A, weighs 78lbs. This is way over kill for a bass boat, but should relieve any worries about running out of power.