Advice on adding a 2nd battery

Tonka Boater

Tonka Boater

Well-Known Member
Jun 11, 2008
3,723
Wayzata, MN
Boat Info
1997 232 BR
Engines
502 MAG, Bravo I
Looking for advice from the electrical experts on adding a 2nd battery... I want to add an AGM to use while on the hook and to connect my new audio system to and I will use the wet-cell as my starting battery. In the picture below I am planning to place the new battery on the port side to balance out the weight.

3 Questions:

1. Is there any issue with spreading the batteries this far apart?
2. What gauge cable should I use with that long of a run? My research indicates that ABYC standards allow a 3% voltage drop (where's Wíngless?). If the batteries were next to each other I could use 2/0 gauge cable with no worries... how can I determine the voltage drop over approx 6 ft run to determine the proper cable size?
3. Can I mix the wet-cell pictured below with an Optima Blue Top?

battery.png
 
For some reason, I can't open your photos, they show a question mark in the frame, noticed that on your post the other day with the new cobalt. I don't know why as obviously no one else had an issue.

Any way.

Your putting the 2nd battery in as a house battery?

Why do you want to join it to the main battery?

Charging only, Or jump starting capacity?


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Hopefully an electrical expert will reply, but I would be concerned mixing types of batteries.
 
IanBat said:
For some reason, I can't open your photos, they show a question mark in the frame, noticed that on your post the other day with the new cobalt. I don't know why as obviously no one else had an issue.

Any way.

Your putting the 2nd battery in as a house battery?

Why do you want to join it to the main battery?

Charging only, Or jump starting capacity?


Sent from my iPad using Tapatalk HD
Click to expand...

Interesting about the pics... I have them stored on my website and I'm just linking to them.

Yes, the new one will be a house battery and I want to join them so the new one will charge and as a fail safe in case the main battery dies.
 
There is a couple of options on how to join them.

Battery Switch. Off, 1, 2, Both

This is not my preferred it is a pain in the ar...... My 330 is set up this way on the starboard. The issue is that I forget to switch to 2 when I stop, or back to 1 when I leave the hook.

My preferred method is to have the batteries Seperate so all the house draw going to the house battery.

You can then use a smart relay or DC to DC (our preferred recommendation) charger to charge the house from the start.

To jump start the main if required, you can join by a Battery Switch, OR a solenoid which allows you to put a switch up on the helm. The twin engine searays came out with them standard, had Tuesday mine on Monday because of the above scenario.

Also check your charger is suitable for the AGM, you may need a Seperate unit.

In regards to the switches Jim has the setups I have listed above, same units I sell here, so will give you a link to the BOE website


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http://www.boemarine.com/categories/electrical/battery-management.html?sort=featured&page=1

Here's the link for BOE

http://www.boemarine.com/categories/electrical/battery-management.html?sort=featured&page=1

Jim sells them in the Blue Seas Brand, we stock them here under the BEP brand as they are made in NZ. The BOE site doesn't show the preset configurations we have here, so I will add another link from the either BEP or the Australian Importer to show you the easy setups.

Apologies I have to add it in another post, if I jump to safari and then back to tapatalk it crashes before I can add the link!

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IanBat said:
There is a couple of options on how to join them.

Battery Switch. Off, 1, 2, Both

This is not my preferred it is a pain in the ar...... My 330 is set up this way on the starboard. The issue is that I forget to switch to 2 when I stop, or back to 1 when I leave the hook.

My preferred method is to have the batteries Seperate so all the house draw going to the house battery.

You can then use a smart relay or DC to DC (our preferred recommendation) charger to charge the house from the start.

To jump start the main if required, you can join by a Battery Switch, OR a solenoid which allows you to put a switch up on the helm. The twin engine searays came out with them standard, had Tuesday mine on Monday because of the above scenario.

Also check your charger is suitable for the AGM, you may need a Seperate unit.

In regards to the switches Jim has the setups I have listed above, same units I sell here, so will give you a link to the BOE website


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Click to expand...

Everything you're saying makes sense for a bigger boat but this is a 20' bow rider and I don't have a DC charger so I need to rely on charging it with the alternator along with my other battery. I'm just looking to wire it the way my previous 2008 240SD was wired.

I have this switch shown below but my big questions are what gauge wire and can I connect a wet-cell to an AGM?

(http://www.amazon.com/gp/product/B000NI58R4/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=ATVPDKIKX0DER)

31jwQXXbB4L._SL500_SS100_.jpg
 
The DC to DC charger sits between the 2batteries, it gives a far better charge to your second battery than a VSR .

My advice is based on your size of boat, and hence the BEP link, these are used in both outboard and inboard installations.

The DC to DC chargers are small compact units


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Hopefully this explains it easier than I.



Mixing Batteries

The reasons we do not recommend wet cell and AGM Batteries together are:

1. When charging, the AGM will reach full charge before the wet cell. This means that the charge system will do one of two things. It will keep charging until the wet cell is fully charged and may over-charge the AGM or it will switch off when the AGM is fully charged which means the wet cell is only partially charged.

2. The wet cell will try to draw power from the AGM and this will reduce the life of both batteries because of under-charging then draining them will naturally damage both batteries but will kill the wet cell quickly.

If both batteries are charged separately, like in most dual battery set ups you can use the two together. With a voltage sensitive regulator or blockout diode (used in most dual battery systems) the start battery is charged first then it switches over to the 2nd or house battery.

The advantage of having 2 AGM batteries is that both can be used for starting or house use in an emergency and quicker charging means less drag on the alternator.

Do AGM’s hold memory?

Lead-acid batteries do not have a memory; however, continuous undercharging will lower the capacity of the battery over time and will shorten their service lives.

Are AGM's dangerous to jump start?

Jump starting from your regular wet cell battery creates gases and sparks which can ignite, making them dangerous. Jump starting from an AGM battery is safe as there are no gases created from the drag on the battery. This makes them the safest battery to jump start from. Please refer to your vehicle owners manual for preferred method of jump starting.

Charging your AGM battery

Float or Stand By

This charging method is used for back-up applications. The battery is continuously on charge and consequently the recommended voltages are slightly lower than cyclic charging so as not to damage the battery. Float voltage for these batteries are about 2.25-2.3 volts/cell or 13.2-13.7 volts. These figures may vary.

Cyclic

Cyclic charging is used in applications where the battery is repeatedly discharged then charged. A higher charging voltage is used but should only be done from an alternator or a 2 or 3 stage automatic charger. NEVER leave your AGM battery on charge indefinitely since it will overcharge and destroy the battery. The voltage is about 2.4-2.5 volts/ cell, or up to 14.7 volts. However you will get longer service life if you use 14.1 – 14.2 volts.

Each battery suited to cyclic use will have a prescribed quantity of cycles to end of life and is dependent on the depth of discharge. Near the end-of-life standby capacity of the battery will reduce. When this reduction becomes persistently regular, this indication can also be used for the time of replacement.

Inverter/Charger Usage

Please refer to your owners manual to ensure that the voltages are correctly set for AGM batteries.

Solar

Solar chargers are fine but there are 2 things to look out for:

Make sure your solar panels are of sufficient size to charge/recharge the size of the battery you are using; and
Please make sure any solar charging system is regulated. Failure to regulate the charge from your panel will result in over charging and subsequent damage of your AGM battery.
Generator

Petrol or diesel generators can be used to recharge your AGM battery, However, it is not recommended to recharge from the charge outlet (if fitted to your generator). As most generators have none or insufficient regulators. This will damage your battery and also void your warranty. It is recommended that you use an automatic charger with a generator that is capable of delivering up to more than 4 or 5 amps, otherwise the battery can not successfully be quickly or fully charged. Please refer to generator owners manual for specifications.

Please remember, FirstStart AGM batteries are charged deeply and speedily by 14.2-14.4 volts from a standard alternator or automatic charging system.

For optimum performance always recharge a battery immediately after discharging.

What to do before storing my battery

When storing an AGM battery in your boat, caravan or 4WD, it is not necessary to leave it on charge. Simply disconnect the negative terminal. This will prevent discharging or draining from any systems that may still be running.
Make sure your FirstStart AGM battery is fully charged before being stored.
Make sure to charge your FirstStart AGM battery every 4-6 months as a precaution.


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Why not just put both batteries next to each other? That's how mine are and there is no effect on the balance at all. Then you have a much shorter run and it looks like there's plenty of room. I would either pony up for two AGM batteries or just buy a group 27 deep cycle from Wally world like I did. Then get a blue sea add a battery kit which has a switch and ACR to isolate the house and manage charging.
 
blaster said:
Why not just put both batteries next to each other? That's how mine are and there is no effect on the balance at all. Then you have a much shorter run and it looks like there's plenty of room. I would either pony up for two AGM batteries or just buy a group 27 deep cycle from Wally world like I did. Then get a blue sea add a battery kit which has a switch and ACR to isolate the house and manage charging.
Click to expand...

I certainly can put them next to each other but the other reason is that the electronics are on the port side and it's a direct run for the wiring. Placement is not a big deal either way and I have plenty of room on both sides but my thought was that I might as well distribute the weight evenly if I have the room and I can keep the house battery closer to the electronics. I like the add a battery kit but the kit alone is as much as a new battery.

Looks like I will cough up the money for 2 new Optima's. Amazon has D34M's for $175/ea and they have 750 cca's... same as my current wet cell.
 
I talked to Optima tech 2 days ago as I had a warranty issue with one of my 3 batteries. Fixed instantly, BTW. I asked if I could run a lead acid battery with the Blue Top AGM as my bad battery was one in the bank or should I swap it out with the solo AGM until my new battery arrived? The answer was no need to swap, the AGM will play nice with the other battery. FWIW.

As to your setup. I would place the AGM on the Port side with a diode protected charging line. No need to go even as big as a 2 cable. The only purpose would be to charge the AGM and the only drain on the AGM would be to the house. Correct? Do you store your boat where it could be plugged into AC? If so, install a solid state charger/maintainer so both batteries are topped off before you go to the water.
 
my DOG HOUSE said:
I talked to Optima tech 2 days ago as I had a warranty issue with one of my 3 batteries. Fixed instantly, BTW. I asked if I could run a lead acid battery with the Blue Top AGM as my bad battery was one in the bank or should I swap it out with the solo AGM until my new battery arrived? The answer was no need to swap, the AGM will play nice with the other battery. FWIW.

As to your setup. I would place the AGM on the Port side with a diode protected charging line. No need to go even as big as a 2 cable. The only purpose would be to charge the AGM and the only drain on the AGM would be to the house. Correct? Do you store your boat where it could be plugged into AC? If so, install a solid state charger/maintainer so both batteries are topped off before you go to the water.
Click to expand...

Thanks for the info... I don't have a way to plug it into AC. The boat is in my driveway for now but our association does not allow me to do this long term so it will be stored about a mile down the road at a storage facility when I'm not using it.


I should have done this in the first place but I sent the following email to Optima's customer service -- we'll see what they say and I will report back in case it can help benefit anyone else:

Hello,

I have a 20ft Cobalt bowrider with a brand new Interstate wet-cell and the boat does not have a charging system other than the alternator.

I am looking to add a BlueTop D34M as the house battery to run our electronics while out anchoring and connect it in parallel with the Interstate wet-cell using the Interstate solely as the starting battery. My plan is to also add a marine battery selector switch so when we're on the hook I can switch to the Optima then switch back to the Interstate to start. While I underway I plan to have the switch set to "Both" so both batteries charge from the alternator.

When the boat is not in use I will set the selector to "Off" so there is no drain on either battery -- is there any harm to either battery with this plan?

Thanks,

Rob


 
Last edited:
No, which is why, yes you can use that switch, but to ensure the life of both batteries, fit one a DC to DC charger, and minimise the position of both batteries to jump start only.




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