Hi Caroline, I use Duracell NIMH rechargeables, and I get excellent battery life. I listen to a lot of mp3's, so rechargeables are definitely the most economical! I don't have to change them that often, and I always have another set ready. I have a one-hour charger that can hold four batteries at a time. I got the charger and four batteries at Walmart for about $25 a year or so ago. NIMH rechargeables have much more life than the older Nicad batteries. Also, you don't have to worry about preserving their "memory"; in other words, you can recharge them before they are fully discharged without ill effects. I occasionally use alkaline and even more rarely lithium batteries. But the NIMH batteries have saved me a ton of money over the years. (I use them for other things, too.) It's great to fall asleep with the book port on and not have to worry about battery drainage, even if the sleep timer is set to zero! Angie