Two separated battery banks

I currently have three SOK 206ah batteries in parallel for my boat house bank. The battery bank has a 10 foot run of 2/0 cables running to the main distribution panel with a Victron 12/3000 Multiplus. I also have a large solar set up. Everything works great but I really could use more battery capacity. The battery compartment does not allow me to add more batteries in that location. I do have space on the opposite side of the boat that would also have a 10 foot run. I do not know the exact length of the original wires as they are buried within the boat structure.
How critical is it to have the same length cables as 10 feet probably has a fair amount of resistance vs the battery banks themselves?
Thanks

The system will work the closer batteries harder. May not get the full output of the farther batteries. IMHO, not ideal, but not the end of the world. You get more capacity, but maybe slightly degraded.

If the cable lengths to both batteries are the same (or very close) it should work fine.

RickL said:

I currently have three SOK 206ah batteries in parallel for my boat house bank. The battery bank has a 10 foot run of 2/0 cables running to the main distribution panel with a Victron 12/3000 Multiplus. I

Click to expand...

So all 3 batteries are located together, right? How are the 2/0 wires for the 10ft run connected to the battery bank? Both + and - to one battery, or + wire to battery 1 and - wire to battery 3 ?

Happen to have a pic?

Warpspeed said:

If the cable lengths to both batteries are the same (or very close) it should work fine.

Click to expand...

That is the issue as the existing systems cabling I cannot accurately measure as it is not accessible. I can estimate 10 feet plus or minus 2 feet. I am considering throwing a shunt in the new bank and maybe adjusting the cable length after some usage. Just a thought. Looking for ideas and brainstorming

MisterSandals said:

So all 3 batteries are located together, right? How are the 2/0 wires for the 10ft run connected to the battery bank? Both + and - to one battery, or + wire to battery 1 and - wire to battery 3 ?

Happen to have a pic?

Click to expand...

The 3 bank is wired correctly with the plus to number one battery and the negative to number three. As I cannot get an accurate measurement of the 10 foot cable (plus or minus 2 feet) that raises the dilema of the second battery bank cable length. I may go with 10 feet and a shunt to se how balanced the system is. My normal current draw is 25 amps with occasional heavy draw. I can then adjust the cable length to try and balance the system unless someone has a better idea.
Thanks

I wonder if you can just measure the cable resistance, and try to match the new to the existing. Would this be measured in micro-ohms?

OffGridForGood said:

I wonder if you can just measure the cable resistance, and try to match the new to the existing. Would this be measured in micro-ohms?

Click to expand...

It may be an option but I do not have the equipment to measure that low of resistance. I am looking at all options so thanks

This type meter will let you measure the micro-ohms. The link is for all 3 types of leads. You only really require the 4 wire leads. It can be had on aliexpress for about 1/2 the cost.

robbob2112 said:

This type meter will let you measure the micro-ohms. The link is for all 3 types of leads. You only really require the 4 wire leads. It can be had on aliexpress for about 1/2 the cost.

Amazon.com

Click to expand...

Thanks. I will look in to it

As a follow up I added the second battery bank with 10 foot 2/0 cables, T fuse and shunt. I have this bank also running through the main shunt. I have been able to track the charge/discharge currents from light loads to very heavy loads and also charging. The current draw is basically split nearly perfect between the banks. Either the "exact" cable lengths aren't as big of an issue as everyone thinks or I got really lucky. Just an FYI for anyone else considering this

What the cable length affects is the resistance of the cable. and this affects balance of the batteries over time as well as the current pulled through a specific cable. Over 10ft a few inches one way or the other won't matter. I suspect it would take a foot difference in this case for more than minor differences to show up. And where you will see it is SOC over time of the battery banks. i.e. one will b 100 and the other 98 and then 100 and 95 and so on, one will drift higher and one will drift lower. And if you see that the correction will be to charge so you are 100 on a single battery then disconnect it and finish the other one.

The other possibility is they will self equalize over time if your usage is sufficiently chaotic enough.

we DIY folks are a bit eccentric and want everything perfectly balanced.

See this post for the long winded form - not your exact situation but the part about two parallel cables is.