I know that in series or parallel that batteries should be same capacity and same age when installed otherwise they will kill each other quicker.

Does that still hold true if you use one of those battery isolator kits that switchs charging from main to auxillary after x amount of time or voltage?

I want to go dual battery but im just planning ahead now if i have to buy 2 new batteries now, or if i can get away with just 1 new battery (one i have in theres only a year old) if get one of those $300 isolator kits too.

 

With isolator less of an issue, but IMHO you would still want same design batteries, like two lead acid, or two AGM (absorbed glass mat).

 

May I ask why you are going to dual batteries?

 

I have a vhf/uhf, cb, laptop (with converter), gps/cell charger, and 7" rear mount (constant on) LCD camera in there. Id also like a winch in the future... and perhaps an amp to run 100 watts instead of 50 on the radio if I get a tri-bander. I dont like the hassle of running everything seperate, it would be peace of mind for me that I always have a spare, or that I can sit and work the radios without having to idle the motor. or disconnect the crossover and run purely off the one battery to avoid alternator and other misc. inputs over the radios without using a filter. plus the cool factor for me, i can pretend its a big cummins diesel when i pop the hood

 

ha - so this requires that the mobile radio platform make it to the top of the highest elevation in the quest to "work all counties" - there was a write up recently on a 220 amp alternator ($349)....

 

Nearly nine years with duals tied together and never had an issue, and I was probably running more amps then you have mentioned so far.
Save you money and buy 2 really good batteries, tie them together and never look back.

 

lol dont think my license allows 200 watts on those frequencies haha I'll double check.

what do you mean tie together, like just have them in without isolator?

 

yep, just parallel - no need for big final amp, just carry a long yagi...