Jun 1, 2009

Ready to test: enhanced battery life forerunner 305

I've always been impressed with the battery life of my forerunner 305. At the JFK 50, it lasted over 11 hours, probably long enough to allow most people to finish the race on a single charge. However, for me, as slow as I am, it was good for about 42 miles - better than I expected to be sure, but not enough. There'd be no way it'd last for a 100-miler, and it'd sure be nice to know for sure I can run it for a complete 50-miler.

Always on the lookout for a possible solution, a post came across the ultrarunning listserv that might have had my answer. Jim O'Neill posted his solution here and I figured I'd give it a try.

So far as I can tell, all the device does is adapt two AA batteries to a standard USB interface. It's so simple, and may be the solution I'm looking for.

I figured the easiest way to put it together would be to use the watch's wristband.

The nice thing about this is I basically have an unlimited charge - apparently, each pair of AA batteries delivers another 15 hours of life. In theory, I can go as long as I have batteries to feed into the thing.

Obviously, I can't wear this on my wrist, so, like Jim, I'm going to strap it to the chest-strap of my hydration pack.

and this is how it looks from my point of view:

To see the data, all it takes is holding up with my hand really quickly:

The only problem with this little setup is what if it rains? The forerunner is water-resistant, but I doubt the battery-adapter is. I've not figured out a way to put that in an super-easily-accessible AND waterproof place in the event of rain. But at least I can keep it dry and still collect data:

..and I can just stick it in the camelback pouch where I'll have it when I need it.

The first real test of this system will actually be a place where I won't need it - the 2009 booty rumble 50K in delaware on June 20th. 50K isn't long enough to require extra batteries on my forerunner, but in the 31 miles I'll be able to assess how cumbersome it'll be over a long period of time. Then, a month later, at the Damn Wakely Dam 32.6 miles in mid July, I'll test it on some more technical terrain. The following week is my 24-hour race in massachusetts, where I will definitely need the extra battery life if I want to collect my pace and maybe heart rate for the distance. Finally, on Labor Day I'll have the Grand Teton 50-miler and I definitely won't run it in its standard battery life, but will want to have a complete log of the race.


  1. That's interesting. Does the watch continue to record data while it's recharging? I've got a solar cell setup I plan to test on an extended backpack trip this month. But my plan is to let the solar cell recharge during the day, then use that on the 305 once we hit camp for the night.

  2. yes, it'll operate the same way while on pure battery or plugged in, and won't skip a beat if you plug it in during a workout.

  3. Get a couple of the newer lithium (non-rechargable) AA batteries and you should be able to go MUCH longer.