Most electric flyers have already moved to lithium polymer (LiPo) batteries for their higher power per volume and lower weight. However there's another option out there which is gaining popularity, namely M1 cells from A123 Racing. These are another lithium-based technology which are supposed to be safer than LiPo, can be charged very rapidly, and can be discharged all the way without damage.
Interestingly, these cells are used in power packs for DeWalt 36V cordless power tools, which turns out to be the cheapest way to buy them (they routinely go for about $100 USD on EBay). Here's a great tutorial on building your own packs, as well as what it takes to charge them. Note that standard LiPo chargers cannot handle A123 batteries, but newer chargers increasingly support both chemistries. If you're feeling less adventurous and don't want to tear apart DeWalt packs, you can buy M1 batteries from MEC in a variety of sizes.
The only apparent downsides to M1 cells is that they weigh a little more than LiPos for the same power. While they're unlikely to find their way into micro aircraft, they are well suited to park flyers and especially to larger models, as well as helicopters like the Century Swift 16. If you plan to use A123's in your next project, remember that each cell delivers 3-3.2V under load, with a capacity of 2300 mah, rather than the 3.7V per cell we're used to with LiPo.
Have you used A123 cells in your fleet? Let us know what you think of them in the comments.
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