Garmin Forerunner 305 battery life question

Hello,

I am considering purchasing a Forerunner 305 to replace my old polar HR monitor, however I am a little concerned about the battery life. The Garmin website says the battery life is 10 hours, but it is not clear about whether this is total run time (ie including non use) or just when it is being used (ie actually training/racing and its detecting HR and GPS).

I normally ride twice a day (am and pm) and am a little concerned that the battery will run out before I finished my second ride (coming home from work).

Does anyone who has a forerunner know whether I should expect to have to recharge it before my afternoon ride (ie is the battery life 10 hours total)?

many thanks in advance