No one wants to put their adventure on hold while waiting to top up their batteries.  If you’re like most of our customers, one of the most important metrics you’re concerned with when it comes to recharging your devices off grid is “How long will it take?!?!?” It seems like this is entirely dependent on the output of your energy harvesting device, be it a WaterLily Turbine, Solar panel, BioLite stove, TEG, etc.
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It turns out, as this blog post will describe, the rate at which you can harvest energy also depends on the device you are using to store energy.  Not all batteries are created equal!
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We set up a WaterLily USB in a small river on a beach on the #east coast trail.  First we plugged in this waterproof light equipped with USB power output.

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The specs claim that the input is DC 5V 0.8A, which equates to 4W.  According to our USB power meter it only pulled 3W, whether plugged in to the WaterLily, a car USB port or a wall charger.

So what does this tell, us?  Well, one thing is for sure, you can’t always trust the specs on your battery! But are we missing out on power? Could the WaterLily provide more than the battery will accept?

The following day we tried a different battery.  (there was no precipitation or snow melt overnight, so if anything the river was flowing slower).  Same stream, same setup, but this battery was pulling in >7W.

The Yellow Battery claims to have an input of 5V, 2A which equates to 10W.  It doesn’t hit that mark when plugged in to the WaterLily at this location, but does when plugged in at home.  This means the turbine is operating at full load at the flow rate for this stream. 3W isn't bad, but 7W is better.  The device you are charging can have a big impact on how much power you can pull from the power harvesting device.

What does it all mean though?

If charge rates aren’t too important to you, NOTHING! Both of these batteries would be full in reasonable amounts of time as shown below:

Light / Power Bank:  Full to 9Wh in about 3 hours

Fospower: Full to 37Wh in about 6 hours

If you are heading out on a multi day or multi week expedition and will be using electronic gear, charge times may be more crucial;  You don’t want to be waiting on your battery to charge before breaking camp and starting another day of adventure. (or, maybe you’re like us and just obsessed with efficiency!)   Whatever the case may be, if charge rates are important to you, be sure to understand the specs on the battery you plan to pair with your WaterLily. It’s not a bad idea to pick up a USB Power Meter to see how your batteries perform  before heading out. It’s also handy to have one to help find the optimal mounting location for your WaterLily turbine.

Questions of comments?  Let us know!

#rechargewithnature