Can you have too many batteries?

Agree with you Jeff, that is why the comment above about never being able to charge the batteries was made in the original comment. Seldom do people realise the voltage drop across 6mm and even 8mm cables make it a surity.

Just threaded a house supply cable through a land cruiser recenly, in conduit of course, to make sure there was no voltage drop. Same on the trailer but just some 8mm to join it for half a metre round the trailer likage.

JohnR, No matter how large the cable is, you will still have a voltage drop, it will just be less. The problem is not just how large the cable is, but also how LONG the run is between batteries.
While charging, check the rear battery voltage against the voltage at the front of the vehicle and if your rear battery is low, there will be at least a half volt drop or more depending on how low the rear battery is.
Cheers

drivesafe, you are right to an extent that the alternator has to run long enough. We are talking cables as big as you little finger including insulation, or without the insulation for the cable I have if I want to use it. When you have voltage drops of several decimal points, you are talking none in the scheme of things. The supply cable in the LC we put in is begger than many jumper leads you can buy. You can look up the LCOOL chart if you really want. The drop is stuff all.

I have some 400 amp welder weight leads if I want to get serious. The main problem is the quality of clamps.

Just an addittion to JohnR's comments,
The cable was 25 sq mm which was second hand. We used to drag 240vac through it @ up to 130 amps no probs. 3 cores of the stuff ran our dairy for over 13 years
The lcool calculator says the drop is nine tenths of bugger all.
once it was in conduit twas fun getting it up the chassis rail!!!
with a slight change to the ends it should power a winch I expect

NickR

Hi JohnR and NickR, I am not saying you are incorrect to use the heavy cable but you will find that there are some differences between 240 AC operations and 12 Volt DC. With long cable runs at 240 volts AC you can loose 10 volts and have no noticeable difference in the operation of equipment. This is only a 2.4% drop.
Even with heavy cable, because of the distance, a 10 to 15% voltage drop is common place and as I posted earlier, wait till you have a low charged rear battery and once you start your vehicle, measure the voltage drop and you are in for a surprise, NO MATTER how thick your cable is.
My point was that ANY size cable can be used but yes your thicker cables is better but most people can get by with the cable size posted originally.
Cheers

ds, I suggest you come and check the cable to prove it wrong mate.

25mm square cable is a long way better for the charging than 8mm which is the point I made earlier. I am aware of the difference between 240v and 12v or 13.8 at charging and once again the voltage drop is minimal in comparison to 8mm cable, even over 4 metres.

I have seen many times voltages of 100 metres for 240 volts with less than that because the drop has been calculated for the current draw. Bigger cable you may understand

That said we still see people use 6mm and it will still slow down the charging over a distance longer and it takes longer because the voltage drop is greater as you acknowledge - actually you don't acknowledge.

Most people I know can understand the analogy of trying to force 1000 litres of water through a half inch pipe versus a 2 inch pipe. It will take a hell of a lot of pressure/energy or time to get it through the half inch pipe in comparison to the 2 inch. ds 12 volts is low pressure electricity.

Too small a cable will reduce the capibility of charging or over a distance allow heat to build up and burn the insulation and possibility the vehicle if the draw is too high. If you chose to use a small cable from the front of a vehicle to the trailer you will find the battery doesn't charge even if you drive the daylight hours, running the fridge as well, because of the voltage drop. That is the reason why some may think they need to have a different battery and can't get it charged

Drivesafe> what a load of absolute bull manure "Next, your alternator will easily charge up all three batteries but this will depend on how fast you are going, IE. how fast the alternator is turning. "

Drivesafe you know little about nothing and even less about anything to do with batteries or twelve volt systems. Drivesafe toddle off back to nanny gregor for a nappy change.

Paul while solar panels at this point in time may be outside your budget, have you thought of using a small solar panel to maintain your battery in proper condition and fully charged state when not in use. A 12w solar panel and SHS6 Morningstar solar controller can be had for $230.00. This cost should be recouped in the life of the first battery. For an extra $30.00 you could get the larger regulator SHS10 and add a 110w panel ($715.00) when funds are available.

Hi Paul, don’t forget to put circuit breakers at both ends of the cable near the battery terminals, no matter what size cable you use. If you have an accident or jack knife and pinch the cable, you are going to have a massive amount of current shorting.
Cheers

Drivesafe more bad advice. Drivesafe how about you toddle off and find some proper education in this low voltage automotive field. Virtually every post you give incorrect, wrong, misleading or ill informed technical information.
Drivesafe nanny gregor at overlander babies is calling you