Having backlit screen is probably the reason why it needs lithium battery in the first place, as a simple pack of 4 AA batteries wouldn't last as long. Lithium

Having backlit screen is probably the reason why it needs lithium battery in the first place, as a simple pack of 4 AA batteries wouldn't last as long. Lithium battery has a life cycle of around 1000-2000 charges, and may deteriorate even faster when exposed to high temperatures. Depending on the capacity though, you can expect a cycle to last more for a calculator compared to, for example, a smartphone, so it might not be that much of a problem (but then again you have the backlight, a major drain). When the battery dies, you can't simply go to a nearby store to get a replacement. You usually have to send the device back to the manufacturer to get it replaced.