As you can read on many websites and discussion lists, it will bring about the end of the world if you put two batteries that are not exactly the same in parallel.
Unfortunately for most 4WD owners, this is exactly what we want to do. Even if they are exactly the same using an isolator makes them do different jobs, so when you go to charge them they are no longer the same.
95% of battery isolator systems charge your dual batteries in parallel. Even the ones that claim to be smart – are just a set of relays (switches) inside to parallel the batteries together. (There are some EXPENSIVE exceptions, you’ll know already if you have one).
Luckily it seems from some expert commentary on the topic it is actually just fine. I figure this guy should know what he is on about, seeing as he is now the current Chairman of the IEC subcommittee on Secondary (rechargeable) Batteries. Primary batteries being the Duracell use once variety.
So isolate or charge in peace, parallel is fine.
AÂ far more interesting discussion is optimising charge management, but that’s another discussion.