Sim900 registry and unregistry due to ground cable

After months of messing around with a sim900 module that would register on the network only sometimes.

I've been playing around with the power connections to the sim because the battery pack is indeed outputting 5.05v but when measuring power at the sim terminals it drops to 4.80v or so. I noticed that when interconnecting both ground pins on the sim900, the 3 second Blink is achieved once again. Is this normal behavior for the sim900 module, this registering and Un registering?