Alex replied:

Nigel, for the baffle to be effective, there have to be two things happening. First, it needs to reflect heat back towards the extractors away from the battery, and second, there needs to be an airspace and preferrably a flow of cool air between it and the battery. For the first effect, steel is a decent material to make the shield from. If you can polish it on the side towards the extractors it will reflect the heat better. For the second effect, have an inch or two between the baffle and the battery for air to flow through, and have it open ended, maybe with an extension to the front of the engine bay to encourage airflow through it. CHeers, Alex.

CHRIS replied:

Nigel
For my dual battery I have placed on the bottom of my battery tray a strip of a poly material (similar to white plastic cutting boards) about a half inch thick, around the vertical sides of the battery I have enclosed these with a sheet material of a silica type product approx 2-3mm thick and across the top have placed a sheet of a material similar to the under bonnet insulation that was on some cars This has a reflective foil layer on one side.(Have to watch that this foil layer does not allow a short circuit across the terminals on wet cell type batteries ). I am also using an ODYSSEY ES12V1500 battery because I wanted the biggest battery that I could fit into this tray and because of the tightness of this fit have to use the battery on its side to clear aircon pipework. This also means that I don't have to worry about this short circuit problem as they are now under the inert foam underlay of this sheet. This battery also has no liquid to be affected by the heat generated by the motor and is able to be used in this position. This installation has now been used for almost two years now with no problems in my GU Nissan petrol wagon and we have done some long continuous driving trips as well as day to day use. The battery tray sits against the firewall over the top of the exhaust system.