Hi Tridacna,
The Perdix is about 30% more efficient than the Petrel at the same level of brightness. Depending on brightness, using an alkaline AA battery about 25 to 40 hours is expected on a Petrel and about 35 to 50 hours on a Perdix. The Perdix seems to be operating fine, but the Petrel battery life is shorter than expected.
A common reason for such behaviour is that the battery type setting is set incorrectly. For example, if the setting is set to the '1.5V Lithium' type but '1.5V Alkaline' batteries are actually being used, the low battery warning will occur much too early. You can see what battery type is selected by pressing the right button a few times until the battery voltage is shown. The only way to change the battery type setting is to crack open the battery cap, then re-tighten it. After a power cycle a page will display to confirm the battery type, at which time it can be changed.
If you don't think that is the problem, contact us and we will investigate further.
Bluetooth is unlikely to be the issue here. The Bluetooth circuitry is completely powered down when not in use. While the Perdix does use the lower power Bluetooth Smart protocol, the Bluetooth on time is typically so short as to not have a significant impact on battery life (unless you are doing a lot of log downloading).
Best regards,
Tyler Coen
Shearwater Research