Dual Batteries in Parallel

[Cuppa]

I think it's more the open circuit that might be created if switching between batteries on the fly and the potential for increased voltage through said circuit....

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That’s my understanding too. No probs if switching when motor not running.

See the first paragraph in this link http://constructionmanuals.tpub.com/...s/14273_51.htm

The ON/OFF/ON description of my switch I gave earlier was a bit misleading. It is an ON/OFF/ON switch, but also has a feature called ‘Alternator Field Disconnect’ which protects the diodes in the alternator in the event of the switch being switched to off position whilst the engine is running.

https://www.bluesea.com/products/110...witch_with_AFD


Edit. Just read your 8.30pm post Crate. My apology, you are correct. I had thought you were switching between batteries, as opposed to switching to add a second to the first. An important distinction.