Ah, This brings back memories of my first e-book reader, a Compaq iPaq 3600.
It served me well, and with the extended battery sleeve gave me about 6-8 hours of usage. It was retired when it took a Milk bath (Remember never store liquid in flimsy bottles next to expensive electronics.
)
Still, it did allow me to up grade to a Qtek 1010 smartphone, so it did turn out ok more or less.
I would also suggest trying out a program I've been using since the first Ipaq for reading txt and html files.
Its Called
Lister and can be found
here.
I've found that while the interface is basic, its one of the lightest in terms of system resources, so can run very nicely in the background, when doing something.
And I'll second (or third) the suggestion to get a new battery when you can. I'm not aware of how easy it is to swap them out on your model, but that will probably give you a fresh battery and a spare which you can swap out in an emergency.