I want to clarify something. When I said te MXJO 21700 20A battery is an OK battery, that is according to Mooch's test at the time he tested the battery. And here lies the rub...
Your MXJO 21700 20A battery may not be the same exact cell that Mooch tested. Why do I/we say this? Because it's a rewrap battery. MXJO is not a battery manufacturer, it's a company that that rewraps batteries with their own branded wrap. So when it comes to rewrap brands you never know when they might change the battery they use underneath that wrap.
Some of the most commonly seen rewrap brands are...
Vapcell
Ohm Tech
MXJO
TrustFire
Ultrafire
Keeppower
Epoch
Efest
That's why it's best to stick with what are called OEM batteries (and from a reputable source). The reason is becuase these batteries are manufactured by their respective companies are rarely do they change the specs of the batteries. They are not made to be used by the public but by power pack manufacturers, so the manufacturers can't just go changing the specs of the batteries they make just because they ran out of something lol. the power pack manufacturers need to know what they are using in their power packs.
The most popular & trusted OEM battery manufacturers we use for vaping are...
Molicel
Samsung
Sony/Murata
LG
Panasonic
Sanyo
Sometimes you just have to use a rewrap. For instance in my case if I want a half-decent 18350 battery I have to use a rewap. But all in all, for vaping, you should stick with OEM batteries AND check out Mooch's test on the batteries you want to buy to see what his tests show about the CDR/Amp rating of the battery. Even OEM batteries are known to claim higher CDRs than they really are. Best to find out what that CDR was tested at before you buy it. You can even seek other battery testers besides Mooch if you like so long as they have a good reputation and aren't out to sell you something.