I own a Garmin Forerunner 405 stopwatch which I use regularly to track my running and biking workouts, and my hikes as well. Maybe I should call it on its official name, running computer, as it has a built in GPS which allows it to record my position in every second, measure the completed distance, my HR, calculate my speed, burnt calorie, etc.
Well, measuring and calculating all these is a power hungry thing. That’s the reason you have to charge it more like a phone than a stopwatch – you don’t pop in the small battery and forget it for years but rather charge it in every 10 days or after every second workout. I bought it second hand, it is 3 or so year old now which is fairly old age for a phone battery, and it seems the dying battery problem reached my Garmin too.
It started to became erratic recently only. I usually can track a 6 hour long workout with one charge, but recently it dropped only to 2-3 hours. Sadly, in this €200 gadget the battery is not user replaceable, shame on you Garmin. I’m in Europe, in Hungary, sending it back to the German Garmin for a battery replace would be quite expensive from here as I’d have to pay all the expenses. (Not mentioning the likely language problems.)
‘Help yourself and God will help you too’ say the Hungarians, so I looked around if I can buy cheap battery on eBay or from China. Interestingly apart from the hypothetical discussions about battery life I found very few concrete on the net. I only found a German page where I can buy the battery for €20 + shipping. It's a bit expensive but better than nothing.
Digging deeper into the topic I found something interesting too. In a blog and on a couple of discussion boards you can read an instruction supposedly from Garmin Support about how to recalibrate your battery:
From Garmin Support
The battery of the Forerunner 405 is monitored by the software. If the software miscalculates the battery life, it can appear the Forerunner 405 battery is going bad. Providing a few instructions often recalibrates the Forerunner 405 to provide an accurate reading on your battery, and thereby resolve your issues.
To recalibrate the Forerunner 405 software:
1) Charge your Forerunner 405 to 100%
2) Remove the Forerunner 405 from the charger
3) Start the timer on your Forerunner 405
4) Allow the Forerunner 405 to completely drain
5) Charge the Forerunner 405 back to 100%
6) Wait one additional hour
7) Remove Forerunner 405 from the charger
This method can work in case of the computer battery packs so why not here? The battery type is the same (Li-Ion), and if the problem is software related it sounds reasonable. I’ll try it first before I buy anything. I’ll keep you posted! 
Update (12/08/11) Whoa! I have done only 3 full charge/discharge cycle yet and the result is spectacular: the last up time was 6h14m which is the same time I could ever get out from it !
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