Is it safe to add more batteries on my boat?

[tahmad575]

Hello I hope everyone's having a great summer,

I currently have 2 batteries in my boat, one in the left rear storage compartment and one in the right rear storage compartment, there's also a battery switch (1, All, 2) and I keep it at "all" at all times. Battery capacity is 1000 cranking amps for both batteries, they were new 2 years ago.

I am wondering if I can add 2 more batteries in parallel so that the voltage stays at 12 but the amp capacity would be doubled. Basically I want to have 2 batteries on the left and 2 on the right.

The reason I ask is because ever since my last leak I now leave my battery switch at "all" when I leave the boat for 4-5 days so that the bilge pump runs when it needs to, but when I come back the following weekend the system is too weak, the blower runs the bilge runs and the engine turns over but it's slow and not enough power to turn the starter fast enough to start the engines.

I currently have a 3rd battery as a backup and I use jumper cables to connect the backup battery to one of the 2 installed batteries and the boat starts right up although it takes a good hour of running the boat to charge the batteries back up so that I can have the audio system run while the engines are off and then be able to start them back up with out jumping them. (if I run the boat for 10-15 Minutes then play music when it's off it doesn't start back up with out jumping it again)

Would having a total of 4 batteries be a good idea? I'm concerned that the alternators on the engines would have to work extra hard to charge the system up because it would be twice the capacity or am I wrong on that? Also would having double the capacity send too much amperage to the starters and blow them out?
I'm also planning on adding more speakers and a larger amplifier to my boat in the future so I want to be ready

Let me know your thoughts and suggestions, thanks

 

[Beachbummer]

Why is there a drain in your batteries when you are not there? Fix that so there is no parasitic drain. My humble suggestion would be to add one battery to your "Main" bank, in whatever side you are normally more heavily loaded... AND leave that larger bank ON when you leave it in the water, and run on ALL or Bank 2 sometimes to make sure all batteries are charged.

Is your bilge pump the kind that comes on to "see" if there is water? Do you have a memory power to radio draining power? 5 days (other than if the bilge pump was working hard which is also no-no) should be a piece of cake for the batteries.

You will burn down nothing by having more battery capacity. As long as they are hooked up in parallel, there is no such risk from a "too Much Power" side. You are OK to worry that it's more capacity to recharge if/when it goes flat, but that should only happen with actual power being used (music or bilge pumping). it should not empty on 5 days of no activity, so figure that out first would be my humble suggestion before you add anything.

I have 2 batteries and I try to keep on 1 or 2 but not all to avoid your exact issue.

 

[tahmad575]

@Beachbummer thanks I appreciate the reply, I believe it's the type that checks for water every hour or so. I hear it run quietly sometimes but no water pumps out, ever since I fixed my leak it's only ran once the day after a rain storm I'm not sure where the water is leaking in from but it's very small possibly a couple drips per day? It's been about 4 weeks since I've fixed the leak and the water level In the bilge is below the bilge pump (had a couple of thunderstorms this month) I'm guessing rain water comes in somehow to the bilge my cover isn't the best and despite my best attempts water still pools on the cover.

As for the parasitic drain how would I check that? I keep my radio off with the switch at the helm, I can't think of anything else other than the bilge pump that would drain the batteries

Also what do you mean by add one more battery to the side that I'm more heavily loaded, like which side of the boat has more actual weight so I can maintain weight distribution or heavily loaded as in which side of the battery bank has accessories running off of it ?

 

[biffdotorg]

Best advice as well is an onboard two bank charger for your setup with a Thru-hull outlet.

As you mentioned the "alternator" is actually a stator on each motor. And these stators do not have the output of an alternator. An onboard charger is really a must in most of the multi-battery write ups on this forum. If you don't have shore power on your lift, consider a solar trickle. Anything to supply some juice to at least counter the draw you have going on while away.

Good luck!

 

[Beachbummer]

Yes, that's what I meant about the weight. These batteries are not light at all, so give some thought to how much more weight and where it would be better tolerated.

Since the bilge pump is the kind that comes on to check, it makes sense the batteries would drain some, but no start after 5 days seems excessive. Hopefully others will update their experience. I have a different pump with no auto, and I added a float to trigger the pump if there is water. this set up uses no power while it's not running.

In order to test the amount of power being used by the boat when "quiet" you would need to use a multi meter, in series with the batteries while the load is running, measuring AMPS.
(You would take off the positive from one battery going to the master switch, set the master switch to that single battery, and then connect you tester to fill the gap in the disconnect, one lead to the battery, the other on the cable, so the current would have to travel via the multi-switch..)

Before (Master Switch)+-----+(Battery 1)

During test (Master Switch Set to Batt 1)+---(+Amp Meter-)-----+(Battery 1)

All the load of the boat would be going through the multi-meter. This is very simple, but you must do it only at minimal load on the electric system, not with the engine running or anything else electrical powered up, otherwise the amount of current will be too high and you will fry you multi meter. Your multi meter will indicate how much current it can take. It's usually fine for this test as long as you power everything off!

Best of luck however you decide to proceed. Hopefully others will provide their experience with this pump type too.

 

[Matt Phillips]

Rather than adding additional batteries to run your bilge pump, it's easier to add a method to charge your batteries between visits. Although my 2017 has an integrated solar panel that keeps the house battery charged (I leave my boat in the lake all summer) I needed a different solution for the 2009. I went with a Solar Panel as described here: https://jetboaters.net/threads/solar-battery-charger-install-w-pics.3414/.

 

[JetPowered]

It’s much cheaper in the long run to just replace the bilge pump with a float sensor model and delete the water sensing type.

Edit: yes adding more capacity for stereo is understandable but if the battery banks are continually drawn down to low levels without a good recharge source those batteries will die a premature death.

 

[tahmad575]

Thanks everyone for the helpful replies,

@biffdotorg By lift do you mean the vehicle I use to trailer the boat? My marina doesn't have shore power let alone any power source at the docks, So I wouldn't even be able to have those trickle chargers hooked up to the batteries. Im thinking about buying those portable jump starter batteries as a backup

@Beachbummer Thanks for the advice the amp draw test seems simple enough, I will get back to you on the test results when I do it hopefully by this weekend. Im going to order the float switch type bilge pump as soon as possible ? As for the weight distribution Ill keep my third battery on the opposite side of the helm because I can notice it leaning more starboard when Its just me on the boat with the additional battery on the starboard side

@Matt Phillips Thats a great future the E series models have, I am planning on installing a custom wakeboard tower this winter and I plan on having a solar panel or two on top of the tower for the sole purpose of trickle charging my battery bank

@JetPowered My thoughts exactly, I am going to find a bilge pump with a float switch on amazon tonight, thanks

 

[tdonoughue]

It should probably be noted: the intended operation of that 1, 2, All switch is that you leave it off when away from the boat, on 1 to float, on 2 or all to start, and on all when running. That way you always have the charge on battery 2 to start the engines. And when charging you are in all to charge them all.

Myself, when I had one of those, I hated switching all the time. A real pain. I would get an ACR, that manages that automatically.

The other possibility if you don't have drain is that your batteries may be old and need replacing. But start with the drain. I have 2 batteries, but don't store on the water. I still have never had a dead anything even sitting and floating with stereo and amps running most of the day...

 

[Beachbummer]

@tdonoughue Something I worry about with the ACRs is you don't know how well the house battery will start the boat until you need to try. With the switch I rarely run on Both, but it is a pain to "switch" the switch as you point out. I switch batteries everytime I remember, usually every week or every other if my memory is slow. If I remember half way I set to both and switch again. I feel this way I know for sure both batteries are always well.

I've thought of installing an ACR but because of this I have not. (As my boat is older this was not an included feature way back when)

Any thoughts or concerns?

 

[Julian]

From my perspective, a system with house and start loads separated is ideal (not combined). Also, a bilge pump that only pumps when water is present (float switch type). Finally an ACR to charge both batteries.

From my experience wet slipping with no shore power, a standard battery lasted me 2.5 weeks with the backpressure bilge pump before it would weaken the battery to the point it couldn't start the engines. So if you are getting less than that, its likely your pump is pumping water (you have a leak), or you have a power drain (mine was the radio-so I isolated the pump and switched off the batteries totally).

 

[tdonoughue]

The benefit to keeping loads separated (as @Julian suggests as well) is that you hopefully don't need to find out whether the house battery can start your boat or not. You reserve one battery only for starting. The one that you normally use (for bilge, radio, etc.) does not get used to start at all. If you get in a spot and for some reason the start battery cannot start the engines, you have the option to combine them still. What the ACR does for you is to automatically combine the batteries when there is a charge present. That means that charge goes to both batteries, but then when you shut down, one battery is reserved for starting.

If you always combine, then you have no reserve for starting.

The other thing you might consider is to rewire your bilge to the other side of the switch (and add a fuse, of course). That way, the bilge runs regardless of your switch position (again, hopefully from the house battery). If you do that, you would want to a) replace the bilge with a float-type, and b) make sure you put the fuse someplace handy (because that is how you would then turn 'off' the bilge) or add a switch to do so (or wire to the one at the helm). A float type draws no current if there is no water. Your current model runs every so often to check if there is water. If it detects a load, it keeps pumping. If not, it shuts off. That is great for running on the water, but for overnight, etc., if there are no leaks, the constant checking will drain the battery over time. If you are out of the water and have it hardwired with no off switch, the pump will keep checking.... eventually you will have a dead battery.

Edited to add:
In my case, I left the stock 'checking' bilge (it came wired to the switch at the helm, so you can turn it off) and just added a second bilge that was a float type. Best of both worlds and a backup to boot.

 

[Beachbummer]

Mmmmmm. I will agree to disagree and leave my last thought on the topic. Batteries are disposable/wear item that will die. Otherwise, I would have only one on the boat. My power needs are modest as my Sound system is sad and small, and rarely used.

Hence I like the full back up and dual checks provided by switching the power from one battery to the other, as full operation on a single battery is my number 1 priority. (And many outings over my boating life have been saved as a result, when one battery dies or was discharged.)

I understand this seems a bit caveman and backwards. And that's Ok. In my mind the difference is not huge and I can see how on many cases the ACR can be seen as Superior.

Thanks for the info, I feel I understand your perspective.

 

[tdonoughue]

Fair enough. Hope I have provided some help, nonetheless. Float well.