The CGR18650CH is rated 2250mAh 10A
It's limited to 10 Amps discharge rate. A good rule of thumb is to allow a 50% safety factor for pv's, so for design purposes, figure 5 Amps max.
A fully charged battery is 4.2Volts
R = V/I = 4.2volts/5amps = 0.84 ohms minimum
as long as you're 0.8 ohms or above, a 10A battery is fine
The time it lasts has to do with the mAh rating.
2250 mAh = 2.25 Ah. this means that drawing 2.25 Amps will drain the battery in 1 hour
An NCR18650PD 2900mAh 10A might be your best bet as long as you're running 0.8 ohms or above. Still not going to get much more duration out of a charge.
I've never had a mech or rba but been thinking about it. I think this Is correct, but I'm not certain