PDA battery dead = data loss?

I've had my PDA (ipaq 1945) for four years and I use it daily. The battery was low last night so I put it on the charger before going to bed. I woke up this morning and the thing was completely dead. It won't even come on. I ordered a new battery which is supposed to arrive tomorrow, so hopefully I didn't lose everything. How long does the backup battery last for? Is there a chance that my data will still be there if the PDA is dead for 1-4 days?