The battery can last as long as 10 days, so you won’t need to charge it as often as other Fitbits. But beware that the screen is small, so it can be more difficult to read than other trackers and smartwatches. Doing any type of plank exercise will make your arms stronger, but doing plank-ups is especially effective for strengthening the triceps and biceps muscles in your arms. Using a map, y…