while it's cheap anyway don't be surprised if you come to use them at a later date and some of the spares have failed already from just sitting around, shelf life is generally not good on these, they need to be used
I fully expect that, but with them costing USD4 each, it's a gamble I can afford. Interestingly enough, I had an old shoe box full of old 300ma LiPO batteries that I used extensively on my UDI mini quadcopter from 2+ years ago. Recently, I gave all the small drones to a friend (I've upgraded to the various DJI models) - and charged a few of the batteries for him. When demonstrating/teaching him how to fly them, I was surprised to see that the batteries all worked as good as new (flying for 5-7 minutes). I would have thought, given their age and lack of use, they would have ballooned out and failed. But they hadn't... They're just slightly thicker than the ones in the 0806, else I would have used them.
From the drone forums, the consensus seems to be that LiPO batteries fail more quickly if they're kept a constantly full charge. In fact, DJI has updated the firmware in the controllers installed in each battery that will automatically self-discharge the battery to 50% if it has been at 100% for more than 3 days. My initial "smart" batteries I had for my Phantom Plus ($130/per battery) failed after just 8 months. I didn't know not to store them full. The battery swelled and died. DJI refused to warranty them (only 6 month warranty on the batteries, anyway). Lesson learned.
The replacement 0806 battery that arrived today was nearly depleted (according to the battery symbol and the 'low battery' warning on the 0806). When I get the other spares in, I'll make sure they're not fully charged, and will put them in storage.
A far more likely scenario is that by the time another battery fails, I'll have forgotten about these four spares (or will have misplaced them) - and will end up ordering more. That' s the way I roll, unfortunately.