I found this on the internet:

Turns out that the Zoom Q4 uses a Samsung SLB-10 (SLB-10a) style lithium battery. So if you run an internet search for that battery, you will find spare batteries in the $10 to $20 range. I just purchased one and I was also able to purchase an external battery charger (AC or 12v CIG) -- which is more convenient than having to use the camera as a charger!