Which battery for my ARB locker compressor

[vk2icj]

I have just had my lockers installed by my local Diff mechanic. I need to install the air compressor. I am looking to install the compressor under the passenger seat and was reading through the directions (I know who does that?) The directions state that for 12 volt systems with 2 batteries you should use the main starting battery and not the auxiliary battery. Now my Aux battery is accessible in the cab where the compressor will be mounted and to me seems the better battery to use. Is there any reason not to use the auxiliary battery?

Chris

[ARB87U]

In most dual battery setups the aux battery is only charged when the starting battery is at 100%. As such it is possible to deplete the aux battery and have no power to the compressor and unable to use the lockers depending on the usage of the starter battery and its levels. Of course the starter battery will either always have sufficient power or it will switch back to charging it.

[Deezelweazel]

Easy to explain.
The start up current for the compressor is very high and the working current is also not that small. Usually the engine battery is loaded directly from the alternator- so these current can be delivered directly on demand if not stored in the battery. Due to the short connection the voltage drop isn't that bad.

Supply batteries have:
a) a different discharge curve- long time discharge with low currents
b) they are not always charged, so the discharge can cause damages to the battery.