OK .... pro's and Con's ....

Looks like to me the Combiner would be a more simple hookup?

Two batteries with one switch and on onboard charger.

For a 2nd battery, the 200A relay (combiner) seems best to me. 100% disconnect, where as the isolator will have a small current loss across the terminals. (According to the guys on audio message boards from my search, so don't hold me to that.) The relay is a mechanical disconnect, hense 100% isolation.
You can buy 200A relays for your application a heck of a lot cheaper than the Blue Seas one.

I just got my Stinger 80A relay last weeked from here; http://www.hifisoundconnection.com/S...9420/SFV/30046.
I just needed to disconnect my amps when stereo is off to prevent battery drain. For your 2nd battery use, get the 200A model.

PAC 200 is another brand, but possibly the same as the Stinger brands, which are really WHITE-ROGERS with stickers over the W-R stickers.

http://www.white-rodgers.com/wrdhom/.../R-4005web.pdf

Is your charger a 2 bank?

I dont have an onboard charger right now and also looking at that option ...Seems with a combiner, one output would work however a bad battery could cause problems ... I would rather split the charge cycle.

US1 looking at your relays,isolaters ....they are either on or off ? The Blue Sea type Closes at 13.3V (charge) and then opens at 12.8 Volts and also has a time delay to prevent rapid cycling ...they are pricey ... I agree .... Also with a 2 output charger you would have to Disable the Combiner during the charge cycle ....... good stuff ......m