I don't run isolators on race cars, for two reasons. First, a battery isolator is basically just a set of high current diodes. And a characteristic of a diode is that when the diode is forward biased, (conducting) there will be drop in output voltage compared to the input voltage, of around half a volt. This means that the battery will never see the full voltage being supplied from the battery charger, and for some of the new battery chemistries, that's a problem in itself. Secondly, in my experience they are somewhat unreliable and have a habit of failing at the worst possible time.
For drag racing, I also like to run the fans and water pump between rounds. So what I do, is use an Andersen connector on the connection to the fans and pump. I can connect it to the cars electrical system or in the pits I can connect it to an external DC power supply that is powered by the generator in my trailer. That way, I can run the cooling system as long as I want, and never run down the batteries in the car.
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