Everyone is talking about how fast the 4G LTE data speeds are but most people seem to have forgotten that 4G was supposed to bring a new VoIP-based calling to replace the old circuit-switched 2G and 3G systems. So, why isn’t Voice-over-LTE (VoLTE) here yet? The answer seems to be battery life.

In the US, one carrier does support VoLTE and Spirent-Metrico ran tests comparing it to good ol’ CDMA.

What they found was that the power draw from the battery during a VoLTE call was double that of a CDMA call and (unsurprisingly) the phone lasts only half as long. The test were ran on an LG Connect 4G, which has a 1540mAh battery. The tests were done with Wi-Fi and Bluetooth off.

What Spirent speculates is the cause of the issue is that LTE data modems aren’t as power-efficient as simple CDMA voice transceivers (LTE is a new technology, while the older tech has been optimized for decades). The conversion from voice to data and back to voice is also more demanding.

The Spirent team also ran tests with simultaneous voice and data and found that using LTE for both is slightly more efficient than running the CDMA radio for the voice call and the LTE radio for the data connection (no surprise there).

LTE modems will continue to improve as will carriers’ coverage and, eventually, we’ll get phones that handle VoLTE as easily as current phones handle regular calls.