MKR1000 doesn't provide battery backup when attached to MKR Ethernet shield


I am using MKR1000 for continuous temperature monitoring for my project. I have attached 1500 mah lipo battery on MKR1000 for backup in case its main supply goes off for some time. Lipo battery used to provide backup for about 6-7 hours.

Now I have connected MKR1000 with MKR ethernet shield for better connectivity which was not available on WiFi.

But now my lipo battery is not providing backup for even a minute.

How can I have backup on MKR ethernet shield in case my Vin supply is interrupted.