I just started dabling in the new rechargeable alkaline battery format...Rayovac Renewal. I was becoming concerned with my battery usage and felt worse each time I threw a standard alkaline away. I've always steered clear of the traditional NiCad rechargeable batteries for possibly erroneous reasons. I always heard that when they began to fail that they failed in a hurry (unlike a standard alkaline whose decline is gradual and predictable) and because of the infamous "memory" issue. Seems that (at least in the old days) it was advantageous to "deep discharge" the battery every so often before recharging it for maximum results.
Using batteries with these qualities in RC cars, household flashlights, calculators, and other non-critical capacities sounds great, but I sure didn't want to be caught recording a show and my NiCads that were fine a moment ago are dropping like flies. And, I really didn't look forward to remembering to fully discharge them in time tight situations. If you're like me, you grab the quickest source of energy before a show. Sometimes, flying to a show from work I am forced to stop on the way there to grab a set of batteries! How would I ever remember that 3 days before a show I should leave the flashlight on or drain my 4 D cells to "deep discharge" and on top of that remember to re-charge them?! ;)
So, I waited around a while and read a few reviews of them and finally bought a Renewal power station and a few sets of batteries. I generally use them in my flashlights (as I am now a proud owner of an Eco-Charge unit for powering my D7 and SBM). There a couple of facts that make sense to me. First, their component parts are not as bad for the environment. Second, their voltage "sustain" is very similar (if not identical) to traditional alkaline batteries. And third, they do not require a "deep discharge". In fact, the packaging suggests that they battery will enjoy a longer life if they aren't fully discharged. You can throw them in any old time! The "smart" charger is convenient as it knows when the battery is fully charged and will cease charging when it is no longer useful.
(BTW, I bought my full-size charger and three packs of batteries at Target. The charger was on sale for $20 and with the UPC for the charger and three packs of batteries you're entitled to a $10 rebate.)