Ooma advertises "
a 10-hour talk time and a 150-hour standby time" for both the
HD2 and
HD3 handsets. However, AAA batteries (for the HD3) usually offer less than half the capacity of AA batteries (for the HD2). So, unless the HD3 also consumes half as much power, its standby time may be closer to 75 hours.
Leaving the handset in the charging cradle when not in use, (or otherwise recharging batteries before they are fully discharged), can
temporarily reduce the battery capacity (thereby reducing the standby time), but fully discharging and recharging the batteries a few times should fix that.
The maximum rated capacity for different batteries varies, (usually between 600-1,000 mAh for NiMH AAA batteries); the rated lifespan varies too, (usually between 500-3,000 charging cycles). Higher capacity batteries generally have shorter lifespans, so they need to be replaced more frequently.
Overcharging batteries can
permanently shorten their lifespan, and deteriorate their performance. The charging cradle is supposed be "smart" enough to prevent this from happening, but some users prefer to use an external charger instead, to charge their batteries.
To reduce power consumption, avoid using the speakerphone, turn down the display brightness, and set the display to turn off when not in use. If the handset doesn't need to ring for incoming calls, then consider turning it off completely, and turning it on only to make or receive calls.