There are a myriad of options here depending on the exercise duration and the requirement to use the screen information. The scope will also depend on the phone and its hardware, in particular the screen. So some trial may be needed to find the best settings.
For shorter duration events (1-2 hours) the screen can probably be kept on all the time. This can be set via settings > ’On while active’. Note this does not change the phone display settings but overrides the display timeout while MikesTracker is in view. The phone brightness settings are not altered or changed. Hence some extension of time/reduction in battery use can be achieved by setting a lower brightness. However the screen visibility may be poor outside at lower settings and the MikesTracker screen timeout (see below) may be a better option.
‘On while active’ is also likely to be the preferred option with a Zephyr heart rate monitor - so a quick glance can see if the bpm is within the target zone.
If battery life is a concern the next alternative is to set the Mike’s Tracker screen timeout (from 1-60 seconds). This does not deliver the duration achievable using the phones’ screen timeout but has the big advantage of quickly coming back into view with a tap on the screen. The screen is not actually turned off but the brightness is set to the minimum possible to reduce battery consumption.
The longest durations will be achieved by de-selecting the ‘On while active’ option. The tracking will continue after the screen times out. Note that the display of the track being recorded will be interrupted when the phone turns the screen off. The service routine that records the data will however continue to run. This is not the case for all tracking apps, including some from major players!
The GPS settings can also have some impact on battery use – but not in all cases. On some phones the GPS is turned off between fixes for update times longer than 1 second. The GPS settings also impact the file size. Settings of 2 seconds and 10m gives good resolution. For reference 10mph is roughly 5m/s (or 10m in 2 seconds). For faster activities (assuming a 10m resolution is wanted) a faster GPS setting could be used and conversely for slower activities a longer GPS time setting might be selected. An hours activity at the default settings gives a very acceptable file size around 120k or 360k if heart rate data is also being recorded.