Most lights you'd want to use as a cavern primary won't make good backup lights for cave. And most cavern dives aren't really very well lit in the daylight zone.

If you think you might do cave later invest in a top notch cave light - they serve as AWESOME cavern lights. It's kind of cheating at the cavern level though if you can see everything well.

Or if you plan to stay cavern for a while buy a GOOD cavern light - as bright as you can afford. HID or with as many D-cells as you think you can carry.

Somebody's old canister light you can get cheep because they are trading up to HID would make a good cavern light.

Even cheep HID lights come with chargers and batteries included. At the cost of D-cells you might do well to rent a canister light at $10 a day rather then replace batteries often. Rechargable batteries will save you the cost of the whole light in about a dozen trips.