No,These batteries would be 9v.
Three serial regulated Li-ions have 9 volt at rest (no load).
Under a load of 1~1.5 Amps they will drop to 2.5 volt each. Similar to primaries.
Remember you are getting power from built in circuit board not directly from battery and those boards are not capable of same current delivery as bare cell.
Another world, you won't gain anything if you use 3 of 3 volt (NOMINAL) batteries (even if they fit in 100mm space) compare to pair of protected 18500
This is my experience.
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