Battery capacity and manufacturer's runtime figures are useful context, but they do not guarantee a full day of every workload. Main-screen use, cover-screen behaviour, navigation, brightness and network reception all influence endurance. Compare the way you use your current phone with the pattern you expect on the Flip8. If you spend long days recording or gaming, look for evidence relevant to that workload instead of relying on a maximum playback figure.
Check supported charging methods, adapter requirements and the supplied cable. A powerful charger does not force the phone to accept more than its supported rate. If you travel with a bank, confirm a compatible setup and include its weight in the portability comparison. A compact phone plus a large accessory may still be the arrangement you prefer, but it should be a considered trade-off rather than an unexpected necessity.