There have been some problems reported with malfunctioning switches on the UT02.
(see posts #76 and #33) Discussion of compact size production throwers 700m+ under $60 - #73 by KawiBoy1428
Also:
- M8 is slightly smaller than UT02
- M8 cost $15-$20 less than UT02
- M8 has ramping, UT02 does not, some people like ramping better.
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Personally, I’m considering the Manker U22, a more compact version of the UT02.
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I don’t think many are seriously considering modding the tube unless they already have the know-how and the tools to do it.
Modders often bore out tubes for different battery fitments and it’s not a big deal. It costs no money if you already have the tools.
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To prevent corrosion you can paint or clear coat the inside of the tube after machining, or just apply a light coating of silicone grease inside.
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Or just get a cell that fits, such as the Efest purple 4200mAh or Basen 4500mAh: