Recently, my Garmin 630 has been running through its battery charge really quickly. It should go through a whole week of 4 runs of 30mins to 2 hours (say 6-7 hours total) with use as a smart-ish watch the rest of the time and comfortably have 30% charge left. This last few weeks it has done one 90 minute run with about 20% charge drop and then the rest has gone sometime in the next day.
In trying to get to the bottom of this I raised a Forum question and got some good advice, both here fetcheveryone.com/forum__61043__garmin_battery_problems
and from a link provided by larkim to this thread fetcheveryone.com/forum__57342__14__garmin_vivoactive
I also did a bit of research (as in I Googled it) and came up with some useful advice on how to maintain your rechargeables in the best possible condition
You might only get 300-500 full charge/discharge cycles out of a Li-ion battery, the kind we have in our Garmins. 300 weeks is quite a long time but you can still maintain and improve your battery life and avoid actually shortening it.
1. Avoid letting your battery fully discharge
2. Don't leave your device on the charger for extended periods of time, if possible disconnect it as soon as it is charged.
3. If possible only charge to 90% most of the time and occasionally 100%
4. Avoid letting your device get hot - cooking your battery reduces its life, so don't cover the vents on your laptop or leave your watch on a sunny windowsill, and maybe take the extra cover off your phone when watching YouTube.
5. Avoid regularly discharging the battery completely. Charging up from being part discharged is fine as there is no memory effect with Li-ion batteries.
6. Don't use rapid chargers. In fact the lower voltage you use the better. Even a small change from 4.3v down to 4.1v can make a significant difference to the life of your device. You can check your charging device's voltage output using an App like Chargie on your phone to see what comes out of different charging ports - e.g. connecting to my laptop, it's putting out between 4.0v and 4.2v.
I realise I've been cooking my watch battery by leaving it on charge overnight. From the advice I've got here on Fetch doing a hard reset could fix a possible problem with the device keeping some processes switched on when I think they are off. That could cure it and I'll hopefully get a couple more years out of my watch.