Smaller battery for iriver h120

[Germs]

Hi,

I wonder if I can replace my iriver h120 battery 1700mah/3.7V with a 850mah/3.7v
I know the battery life will be divided by two and that is ok, but will it works as usual, and what about the charging?

I want to integrate my iriver in a portable rig, so I removed the case but it is still a bit too thick.
If I can use a smaller battery and put it where the screen is, it would be perfect.

Thanks.