An excellent manual can opener is the Chef’ Ez Squeeze One-Handed Can Opener.  It has become my go-to can opener. With it, I don’t need batteries or to plug in a charger. You open the handles, place the cutting head on the rim of the can and squeeze the handles repeatedly.  Each squeeze pierces the edge of the lid and advances the jaws around the can. I have had no problems operating the ratcheting mechanism.

The only negative is that removing the opener from the can by spreading the handles seems to always pull a sliver of metal up. Be careful not to brush the top of the open can because the sliver is sharp.