Here comes the "told you so" speech:
If you think the TN4A is impressive, imagine a light that is even smaller and less expensive with similar illumination performance. See post #11 above.
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Now, on to solve your battery problem...
Walmart usually carries a 4 pack of 2400mAH Duracell branded pre-charged, low-self-discharge cells, that are very likely rebranded eneloop XX cells. Look for cells that say "Made in Japan" on them. Usually ~$12 for the set. I'll let someone else advise on chargers, I don't keep track of NIMH chargers. I'd be tempted to advise a nitecore dual-chemistry charger so that you have some freedom to expand to 18650 powered devices later on already built in, but there may be other superior options.
I'd agree with mdocod. I have the nitecore intellicharger I4, and although it is a little slow compared to others, it may actually be better for the batteries to charge them at a lower rate. I like its flexibility in its ability to charge Li-Ion, or NiMH. Whichever charger you choose, I wouldn't get one unless it had the ability to also plug into the car's cigar lighter port. This will extend its usefulness during power outages, so that you can recharge your batteries each day, after you use them all night.
I also agree with mdocod, and MauiSon, that a Convoy C8 driven at 2800ma with an XM-L2 emitter is a great light at the price of about $16. The Convoy series of lights is one of the few exceptions to the rule of low cost lights. The simplicity of a single 18650 battery rather than 3 or 4 AA cells (for the same performance) is a big deal for me. I much prefer the 18650. Since there are few AA lights that will significantly outperform your TN4A, when you want something more, you'll most likely go to 18650, so you might as well get a charger than can do both, Li_Ion, and NiMH.
Good luck with your light, and enjoy!
BTW... 2,376 "whose line is it" points to Amelia for such well though out, and well written posts! :thumbsup: