How long do handheld batteries actually last?

It depends entirely on the chip’s draw, which is why the honest answer is a band, not a number. Light emulation on an efficient device can run many hours; modern AAA at a high TDP on a PC handheld can drain a big battery in under two. Battery capacity (watt-hours) is only the size of the tank — range is capacity divided by watt draw. Manufacturer figures are best-case, measured at low TDP and dim brightness you will not use. Read the reviewer’s band at realistic settings, and plan a charger or power bank for long sessions.