Externally Mounting Battery

Just wondering if batteries need any special protection when they're mounted outside the cabin or not under bonnet?? I'm building a 2nd batter holder and the battery is going to sit under my rear tray, well up out of the way of sticks and stones etc, but it will still get wet, may be partially submerged during creek crossings and may get some heat from a nearby muffler.

I'm wondering if I need to house it in a battery box??

Thanks in advance.

I am also kken on the responses to this as that was my plan

Maybe I should have done some reading beforehand, but I've found out that heat kills batteries, however hopefully that shouldn't be a problem as the battery should have lots of fresh air gushing all around it most of the time and should pretty much always sit in the shade.

More heat there than in the bonnet??

Heat from your exhaust could easily be averted by a simple heat shield. If your worried about submersion then get a sealed maintenance free battery that should in theory not care about submersion.
Just remember that your not always going to get fresh flowing air. It could be sitting idling so heat shields would be a must if your anywhere near the hot exhaust

As Aussie says, get a sealed unit. Gel is ok, AGM is better. That takes the worry out of foreign fluids getting into the battery. And that heat shield idea is excellent too.

The issue of heat in the engine bay is different to heat under the tub but perhaps not for the reasons you might think. If the battery in the engine bay starts to degrade in performance, you know it when the engine starts to crank over slower. The aux battery system never does this, and a battery that has only 20% of its usable life left will still kick-start the Engel in the tub so you might leave for your trip thinking everything's sweet only to find disaster has struck.

For that reason, you should spend a little extra and do things a bit better than you might normally do them. Use 8 sqmm cable instead of 6 sqmm for power going in and out. Have a point somewhere in the tub where you can toss a multimeter or have a permanent voltmeter sitting in the corner (connected by a "momentary on" switch). Even better - get one of those adjustable low-voltage warning lights and stick it in the dash. Have it go off if the battery voltage falls below 12V (12.2V is considered about 50% charge).

Also consider this (it will help ease your mind) - if you're wading through water, that battery under your bonnet will cop some wet as well, and thousands of 4WDs have done this without killing their batteries, so as long as the battery is protected from most physical damage it should be just fine.

How are you charging it? Isolator? Don't forget to use thermal-resetting fuses as close to both batteries as possible and make sure the cable run between main & aux batteries is protected from stray sticks/stones/snakes/wombats/pensioners/scrap metal merchants etc.

Thanks for the thoughts and advice guys. I've got an AGM battery so I should be OK there. Think I have a sheet of 3mm aluminium plate out in shed as well, now that should be pretty good for the job at hand.