It's a prototype device for software development, not a shipping product.
Wrong on both accounts. The MX4 has been a shipping Android phone since September of last year. The Ubuntu phone is the exact same hardware.
It might have a substandard battery.
It does't. GSM Arena stated about 16.5 hours talk time, ~14 hours web browsing and around 9.5 hours for video playback. For the time of the battery benchmarks it was no worse than most other phones.
Such problems would not stop its deployment as a development device. It could be any of these problems and it's pretty pointless to speculate further.
Except it's not a development device.