Dual batteries

Hi all just installed a twin alternator and battery set up, should the negatives on the batteries be linked ? As in auxiliary battery to starting battery to earth ?
Cheers Ian

yes negatives to a good earth.
just a heavy relay from the live to the main battery

Is there any reason why a twin battery setup should not have the two batteries permanently linked? My set-up has a button switch to connect the two, but due to a stroke of genius on someone else's part the radio only works if the two batteries are linked. Hardly a major trauma to flick the switch, but I just wondered if I could by-pass it altogether.

overdrawn said:

Is there any reason why a twin battery setup should not have the two batteries permanently linked? My set-up has a button switch to connect the two, but due to a stroke of genius on someone else's part the radio only works if the two batteries are linked. Hardly a major trauma to flick the switch, but I just wondered if I could by-pass it altogether.

Click to expand...

I run my 2 batteries connected full time

overdrawn said:

Is there any reason why a twin battery setup should not have the two batteries permanently linked? My set-up has a button switch to connect the two, but due to a stroke of genius on someone else's part the radio only works if the two batteries are linked. Hardly a major trauma to flick the switch, but I just wondered if I could by-pass it altogether.

Click to expand...

If you permanently link the 2 batteries you have just defeated the purpose of having the twin batteries on a split setup. You may as well just install a bigger single battery, or 2 medium/large batteries in parallel. If you permanently link batteries they really need to be identical and of the same age, ideally the same batch or else you can create issues and won't get the full benefit and you will almost certainly reduce the life of the "bank". Do you need the split system?

I needed a new battery last year and considered 2 smaller Yuasa 550CCA batteries and linking them in the battery box, thus giving me 1100CCA and about 160Ah, it also worked out cheaper than buying an equivalent spec single battery, however, I thought about it carefully and decided that there was no point, if one battery fails, depending on the mode of failure there is a chance it would take the other battery with it, a bit like battery banks dying because of 1 bad battery. If a plate failure in 1 battery occurred, current would then flow from the good battery discharging the whole thing and also potentially getting so hot it catches fire.

In your original post you call it a "twin alternator and battery" set-up, do you actually have two alternators or do you have a split charge system?
In either case, the earths just need to attach to the chassis, not the other battery.
I had considered fitting a supplementary alternator to mine, using the redundant air-con drive belt, but a split charge was a lot simpler.