The leisure batteries and the engine battery are two different things. The engine batt needs a high current to start the engine. And will be loaded by the alternator. My preference is to keep this out from the leisure.
i advise if you are technical to read out component location from engine cooling,,Emission control, intake air distribution and filtering, Electronic engine controls.fuel charging and controls- turbo charger. And how it works.
They have A Bms. battery management system. to protect the system short use at high and low temp. but they should be whit in the recommend temps. And therefore i did not put them yet in the engine bay. It was too evoke reactions and it did. Will be continued later what super b said to me.