Battery connector question

Bouba

Bouba

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Hi, I am connecting two 80 Ah leisure batteries together in parallel.
The cables to and from the boat to the battery are 95mm2 500v.
Do the cables that I am going to fit between the batteries need to be the same specification ?
 
A little background
The existing battery has failed. I’ve decided that I can no longer lift this 140 Ah 30 kg battery…two 80 Ah batteries will fit in the same battery box. Just wondering what size cable should I fit for the parallel connection ?
 
Bouba said:
Hi, I am connecting two 80 Ah leisure batteries together in parallel.
The cables to and from the boat to the battery are 95mm2 500v.
Do the cables that I am going to fit between the batteries need to be the same specification ?
Click to expand...
Use the same cable. The positive and negatives should not connect to the same battery, positive to one battery, negative to the other. If the battery in question is the Varta in your picture it looks like the cable will not be long enough to allow this, i would use the positive as it is and extend the negative by adding another cable and connecting them to a power post, such as Single Point Power Post

Unless you have a hydraulic crimper, or access to one, don't mess around boding the cables yourself, get them made up.
 
PaulRainbow said:
Use the same cable. The positive and negatives should not connect to the same battery, positive to one battery, negative to the other. If the battery in question is the Varta in your picture it looks like the cable will not be long enough to allow this, i would use the positive as it is and extend the negative by adding another cable and connecting them to a power post, such as Single Point Power Post

Unless you have a hydraulic crimper, or access to one, don't mess around boding the cables yourself, get them made up.
Click to expand...
Thanks for that. My original plan was to have the batteries facing a different way from each other....so the existing cables can reach each battery. The problem is that the cable connecting the batteries in parallel would need to be 75cm long. Yours is a more elegant solution
 
Nick Wight said:
I'm curious as to why you should not connect the positive and negative to the same battery?
Click to expand...
Current will be drawn form the battery with the cables connected to it in preference to the other one, kind of like jump starting an engine. The reverse happens when charging. This cause imbalances between the batteries and shortens their lives. Taking the positive and negative from opposite batteries effectively makes them one big battery and they are both in balance.
 
Bouba said:
Hi, I am connecting two 80 Ah leisure batteries together in parallel.
The cables to and from the boat to the battery are 95mm2 500v.
Do the cables that I am going to fit between the batteries need to be the same specification ?
Click to expand...
Yes.
 
The cables are 95mm2......that makes them virtually impossible (so far) to get them in France custom length with fittings attached
 
So two house batteries parallel with the positive and negative on opposing sides
The smaller cables, say 50mm, connecting the two
Will act as a very low resistor vs 95mm ?
As the smaller cables are v short the resistance / voltage drop is going to be minimal at say 20A ?
During charging would they not equalise ?

🤔
 
Bouba said:
Yes…but I just wanted something online that gets delivered tomorrow
Click to expand...
You wouldn't be able to do that in the UK either, it's not possible for anyone to keep ready made cables on the shelf, too many sizes and an infinite number of lengths, not to mention different size terminals. You'll need someone to make them for you it's hardly reasonable to expect someone to do that on a Sunday and have them with you on Monday !
 
It will be cheaper to pay the boat yard to lift the old battery out and the new one in. Or ask a friend to help.
Or pop to the swindlers and gets a couple of pulleys and rig up a small block and tackle.
Decent batteries last 6 - 8 years these days. Is it worth the hassle of changing the cabling? Big copper wire is expensive these days.
 
kashurst said:
It will be cheaper to pay the boat yard to lift the old battery out and the new one in. Or ask a friend to help.
Decent batteries last 6 - 8 years these days. Is it worth the hassle of changing the cabling? Big copper wire is expensive these days.
Click to expand...
Yes, the cost of the cable is very expensive. The house battery doesn’t last long, because unthoughtful bu99ers unhook your power cable to use the plug....but don’t plug you back in when they’ve finished. So the fridge drains the battery flat and hastens it’s demise.
So, I will bite the bullet and put in two smaller (lighter) batteries....it’s a job I’ve been meaning to do for years...now my back has put its foot down !
I’m off to see an electrician today....they are also a battery retailer and do home solar installations....it’s just a matter of if they have 95mm2
 
Bouba said:
Yes, the cost of the cable is very expensive. The house battery doesn’t last long, because unthoughtful bu99ers unhook your power cable to use the plug....but don’t plug you back in when they’ve finished. So the fridge drains the battery flat and hastens it’s demise.
So, I will bite the bullet and put in two smaller (lighter) batteries....it’s a job I’ve been meaning to do for years...now my back has put its foot down !
I’m off to see an electrician today....they are also a battery retailer and do home solar installations....it’s just a matter of if they have 95mm2
Click to expand...
In that case, spending time and money changing the batteries doesn't fix the problem. It would make more sense to fit a battery saver, so the batteries don't go flat and die.
 
Here’s another question…I would dearly love to have two of these batteries

They are inexpensive, powerful and the perfect dimensions.
Unfortunately they are American (made in Vietnam) and only available in the UK…and while the UK supplier is willing to ship them, it will double their cost.
So does anyone know of a EU supplier for them ?
 
Last edited:
PaulRainbow said:
In that case, spending time and money changing the batteries doesn't fix the problem. It would make more sense to fit a battery saver, so the batteries don't go flat and die.
Click to expand...
That would mean sacrificing everything in the fridge….anyhow, I have moved to a new pontoon that seems to have an abundance of power sockets…so I’m hoping that the problem will go away on its own accord
 
Bouba said:
That would mean sacrificing everything in the fridge….anyhow, I have moved to a new pontoon that seems to have an abundance of power sockets…so I’m hoping that the problem will go away on its own accord
Click to expand...
Sorry, my mistake, i didn't realise your fridge carried on working when someone unplugged the power and your batteries went flat :unsure:
 
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