Batteries on opposite sides of boat?

[DennisF]

I’m looking to add another house battery to the existing one and engine start battery on my Westerly Berwick. I’d prefer not to have all the weight on one side. Is it OK to have one house battery on each side connected in parallel, or would I be better off with house batteries on one side in parallel and engine start on the other????

 

[PaulRainbow]

I’m looking to add another house battery to the existing one and engine start battery on my Westerly Berwick. I’d prefer not to have all the weight on one side. Is it OK to have one house battery on each side connected in parallel, or would I be better off with house batteries on one side in parallel and engine start on the other????

As highlighted.

 

[waynes world]

As above

 

[Sandy]

What about fuel tanks, beer barrels etc, etc or even crew!

 

[DennisF]

What about fuel tanks, beer barrels etc, etc or even crew!

Part of the issue is that most of the storage for food and drink etc is on the same side as the batteries, so there is already a small list to that side. Hence not wanting to make it worse when I add another battery.

 

[DennisF]

As highlighted.

Thanks - that’s what I thought. An engineer friend of mine thought splitting the house batteries either side would be OK, but I worried about having long cables connecting them in parallel.

 

[waynes world]

Thanks - that’s what I thought. An engineer friend of mine thought splitting the house batteries either side would be OK, but I worried about having long cables connecting them in parallel.

that the reason i would keep leisure on one and starter the other. the size of boat though you would hardly notice if all on one side.

 

[TNLI]

I’m looking to add another house battery to the existing one and engine start battery on my Westerly Berwick. I’d prefer not to have all the weight on one side. Is it OK to have one house battery on each side connected in parallel, or would I be better off with house batteries on one side in parallel and engine start on the other????

In general terms it is not good to wire batteries in parallel unless they are of the same type and age, as it can result in uneven charging and if one battery fails it will effect the other battery. It's better practice to simply fit a bigger battery. If you have no alternative then add a house battery selector switch and diodes to any battery chargers to allow both to be charged evenly at the same time.

Practical Considerations - Batteries | Batteries And Power Systems | Electronics Textbook (allaboutcircuits.com)

 

[oldmanofthehills]

In general terms it is not good to wire batteries in parallel unless they are of the same type and age, as it can result in uneven charging and if one battery fails it will effect the other battery. It's better practice to simply fit a bigger battery.

Fitting a bigger battery could make it hard even impossible to get on and off board. I have just duplicated my aux battery with the same H brand 335s and expect no issues for years. I wanted extra capacity to run the ebi while sailing, and that energy hungry chart plotter is also addictive. Its annoying having to turn on the iron topsail daily when the winds are fair

 

[PaulRainbow]

In general terms it is not good to wire batteries in parallel unless they are of the same type and age, as it can result in uneven charging and if one battery fails it will effect the other battery. It's better practice to simply fit a bigger battery. If you have no alternative then add a house battery selector switch and diodes to any battery chargers to allow both to be charged evenly at the same time.

Practical Considerations - Batteries | Batteries And Power Systems | Electronics Textbook (allaboutcircuits.com)

This is, of course, just nonsense.

My bank of 4 domestic batteries weight 112kg, i don't fancy carrying a single 112kg battery down the companionway steps, or anywhere else.

 

[William_H]

Best to have the 2 house batteries next to one another. This means short wires connecting one to another so uniform charge and discharge. It does mean that you need fairly chunky long wires to engine or switch to permit starting with house batteries if engine battery dies. If you do separate the house batteries there is an arrangement where positive comes from one battery and negative form the other (with wires to parallel the batteries) such that neither battery is "electrically closer " to load and charging than the other. So disadvantage is in cost of heavy wiring. ol'will

 

[TNLI]

This is, of course, just nonsense.

My bank of 4 domestic batteries weight 112kg, i don't fancy carrying a single 112kg battery down the companionway steps, or anywhere else.

It's not nonsense, just read the article I posted. If the batteries are all the same age and type, then it's unlikely there will be a problem, but the OP is adding a new battery to an old one, and that can be problematic.

 

[DennisF]

It's not nonsense, just read the article I posted. If the batteries are all the same age and type, then it's unlikely there will be a problem, but the OP is adding a new battery to an old one, and that can be problematic.

For clarity, I did not say that the existing battery is old. It has just been replaced, and I have bought another of the same type and capacity at the same time to increase the capacity, hence my question about how best to fit it.

 

[Stemar]

Having two batteries on either side of the boat will only be an issue if you want starting current from them. I'd guesstimate that 10mm cable would be plenty for domestic loads on most boats, even charging loads when run low. What would complicate it a bit is the need to take the positive to one battery and the negative to the other. If you don't, the battery with the connections will do slightly more work and get slightly more charge than the other, which, over time, is good for neither.

 

[Alex_Blackwood]

This is, of course, just nonsense.

Couldn't agree more!

 

[PaulRainbow]

It's not nonsense, just read the article I posted. If the batteries are all the same age and type, then it's unlikely there will be a problem, but the OP is adding a new battery to an old one, and that can be problematic.

You said:

"It's better practice to simply fit a bigger battery. If you have no alternative then add a house battery selector switch and diodes to any battery chargers to allow both to be charged evenly at the same time. "

That is what is nonsense. No idea where you got that idea from, there is no mention of that in the article you linked to.

Banks of batteries, correctly connected in parallel and correctly connected to the boat work perfectly well and have been doing so since batteries were invented.

 

[billcole]

Batteries in series need to be matched, but if in parallel and not equally charged then the one that's more charged will attempt to have a higher voltage, and so will supply more current to the load, or even charge the less charged battery, so the pair will keep themselves in balance.
Similarly if one gets to be fully charged before the other then the one that still needs charging will draw more current from the charging source until it too is fully charged.
However, one battery could kill the other if it it develops a short circuit cell

 

[oldmanofthehills]

Batteries in series need to be matched, but if in parallel and not equally charged then the one that's more charged will attempt to have a higher voltage, and so will supply more current to the load, or even charge the less charged battery, so the pair will keep themselves in balance.
Similarly if one gets to be fully charged before the other then the one that still needs charging will draw more current from the charging source until it too is fully charged.
However, one battery could kill the other if it it develops a short circuit cell

Though that is true, one big battery could kill itself if a single cell shorted, as does sometimes happen rarely, so the risk is only increased by a factor of 2 in going for paralleled cells. What is more if charging fails due to this parallel bank there is a recovery position of disconnecting the failed battery

The difficulty moving and installing a larger battery could increase greatly.

The OP has a Berwick and batteries are usually under the port bunk which is long and narrow with a long and narrow lid. I had difficulty lifting aboard and fitting a 95AH 20kg 335 in a confined space in such a boat. Two batteries adjacent sorted the problem.

 

[pandos]

I am doing the opposite and putting my batteries together to remove cables crisscrossing the boat.

They may be dense, but if you consider how low down they are and distance from the centreline I doubt their weight will make any difference which cannot be overcome by shifting other stuff around.

 

[TNLI]

Connecting batteries in parallel – BatteryGuy.com Knowledge Base

That article says more about the problems that can occur if the batteries are not of the same age or type, or you get unlucky and one of the batteries starts to degrade or even fail before the other. One check you can do is to check the voltage of each battery to make sure that they match, that will show if one is starting to degrade. As I said before the risks of connection two batteries of the same type and purchased at the same time are minimal, but even if you connection a battery of the same type to an older one, it's asking for trouble in terms of how the pair perform.