Results from a recent study by wireless testing and measurement firm Spirent Communications reveals that voice calls over LTE (VoLTE) consume up to two times as much power as a standard 2G call. This isn’t exactly great news for phone makers and wireless carriers alike but we can expect things to get better over time.

The tests were conducted over LTE and CMDA on an unnamed wireless carrier in two different US cities. Despite the fact that Spirent didn’t list which carrier was used, it’s pretty easy to figure out considering MetroPCS is the only provider in the US that has VoLTE service thus far and a handset to support it. Interestingly enough, GigaOM points out that the LG Connect 4G’s 1,540 mAh battery lines up closely with the device that was tested.

Testing shows that a typical 10-minute phone call over CDMA consumed 680 milliwatts. That same call over VoLTE required 1,385 milliwatts. The company estimated that their test handset could pump out 502.6 minutes of talk time over CDMA. That figured dropped sharply over VoLTE to just 251.8 minutes, or just over four hours. Keep in mind that these estimates were all with other forms of communication like Wi-Fi and Bluetooth disabled.

There’s hope for VoLTE in the future, however, according to Spirent global director of insights Amit Malhotra. As he points out, GSM and CMDA technologies have been optimized during the last two decades to be extremely energy efficient. As such, it’s not exactly reasonable to expect a new technology to achieve that same level of refinement overnight.

“These issues will be mitigated over time, especially as components continue to become more power efficient, and devices do not need to switch between different modes of voice call processing,” Malhotra said.