I am currently using an old lithium-ion laptop battery pack for my portable sound system. The battery seems to work pretty well for its age. I simply hooked up a cable to the positive and negative pins (which I needed to guess) which directly leads into the amplifier. For charging I simply put the battery back into the laptop.
However, is there anything I have to care about? What would happen if the battery pack is empty? Is there an integrated underdischarge protection? And does the voltage output fall over time or is it regulated internally (I don't own a multimeter to test that)?
The pack is rated at 14.8V and the capacity is about 5000mAh.