Efficient 60v to 12v DC-DC
I think this chip is a very good option if you always want an supply from 13s battery. 

I'm seeing that the problem is to get a power supply with 60 V input (max) and low quiescent. Lower input voltage gives more options with low quiescent current. 

With this in mind, a suggestion would be to use a second low power &amp; low voltage battery (1s o 2s) that gets charged from the 13s, and supplies the low voltage electronics, and that totally switches on/off the higher voltage power supply that charges the battery. Its a bit trickier but could also work.