Battery saving during activity

1.) I used GPS only for over a year, but recently tried both GPS/GLONASS. I have not noticed any huge difference in battery usage. I both cases I run five 5K runs each week and will have about 20-30% left on the 6th day.

2 & 3). Pretty sure, no difference that you would notice.

Running outdoors the big battery user is your GPS ... running indoors I notice a lot less battery usage ... but I hate running indoors, so I do it very little.

Max

There will only be a nominal difference between GPS only and GPS/GLONASS but if you're running in fairly open areas and you're trying to maximize battery life the go with GPS only. Other than that the biggest battery drains are going to be the backlight and the optical HRM.

If you're running in the day time turn the backlight off completely so that it isn't coming on every time you push a button to change screens, get a lap alert, raise your arm, etc. And if you're really trying to push the battery life and HR is important to you then get a chest strap HRM so that the LED's on the back aren't on the whole time. If you don't care about HR at all then the oHRM can just be turned off.

Now, with all of that said. As long as you have about 50% charge on the watch a 3-3.5 hour long run shouldn't kill your battery. The first marathon I did with the 235 my hip acted up just before the halfway point and I limped through the last 15 miles to a 4:27 and was only down to 70%-75% from a full charge at the end.

Yeah shouldn't be an issue for a 3-5hr run for sure... ! my wife did a 4:30 marathon with hers, no prob(with optical HR, 1sec record, glonass)

but according to the manual going to GPS only can help, as can Smart Recording vs Every Second, disable auto backlight via wrist...if you were low on battery to start. can also change the settings mid run. Turning off bluetooth might help some (so it isn't looking for or syncing with your phone).

I recently did a 10hr bike ride and had minimal charging needs - was able to turn off 'activity tracking' - which appears to help based on a couple 100mi training rides. maybe.

-edit - changed my recording from smart to 1sec midway through a run this weekend (forgot to change it after my 145mi ride).... and you can clearly see the difference in my run! I will be avoiiding 'smart' from here on out!!!! LOL

I'll be running an 84k Ultra in a couple of months, which I expect to complete in 9-11 hours. I'll definitely use the advice you provided me here, so thanks!

What happens if I run out of battery? Is the activity lost or it gets automatically saved until the point when the battery died?

HR is important to me, but other than that I'll turn off everything else I can, as recommended here. What still puzzles me is the Smart Recording vs Every Second Recording discussion. Supposing I'll synchronize the watch right before and right after the very long (9-11 hours) activity, would smart recording provide any advantage?

I think 235 can charge on the go, can?t it? Try using your charging chip and an external battery pack whilst recording a GPS activity and see if you can top up the battery.

Try turning off Bluetooth as this may draw power communicating with your mobile.
I completed a 10 hour event recently and I still had some charge available and yes you can top it up with the battery pack when on the go.