I use the Cat-eye Octicube, with 4 AA batteries. I've had
no luck with a variety of rechargeables over the years in a
Wisconsin winter, which is when I mostly need a light. A set
of batteries in the Octicube is long lasting (100 hours or so)
and casts a blueish light that is easy to see

=v= I have this, but the AA batteries I use are rechargeable.
I find it frustrating that after all these years nobody has
worked out a bike light with off-the-shelf rechargeables
(AA or C batteries) that you could just plug in. They either
have some proprietary battery or a bizarre proporietary plug
to thwart this.

=v= For seriously dark rides, Light & Motion makes a very
bright light with a large rechargeable batter that fits in
the bike's water bottle cage. Very durable and waterproof --
Light & Motion makes lights for underwater use, too.
_Jym_