A320 battery switch off requirements
 

what are the requirements to switch off the batteries in A320 when the apu is shut down please need a quick answer for this

You can switch them off whenever you like!

However, there will be at least 2 issues.

1. You won't get any fire warning in the event of a fire post shutdown.

2. The APU inlet door won't close.

Good practice (and the AMM) dictate a 2 minute wait between actual APU shutdown and switching the batteries off.

suraj1990
Switching of batteries whenever you feel like is a wrong advice. Batteries should not be switched off of for at least 10 seconds after ADRs are switched off to allow them to memorize the last position. Also they should not be switched off before two minutes from the time avail light goes off to prevent smoke in the cabin at the next APU start up.

A320 battery switch off requirements
 

As above!
The 2min wait coincides with the APU flap being closed. (Ps: 2 min is worst case scenario as APU continues to run for 1 min after use of APU bleed)
However it is the actual de-oilling sequence that is the key factor. The flap closes when the de-oilling sequence finishes, hence the association.
Also when APU start is attempted with apu flap still in uncommanded position (ie. incorrect shutdown) this could lead to APU start fault. (Hence a little wait after master on does not hurt)
My 2cts