I don't think it's all that much doom and gloom for NiMH batteries. My Avalon can charge the hybrid battery from near zero to full in the time it takes to make it half way down a mountain pass. That's pretty fast charging in my opinion.
Also I was under the impression that NiMH was less damaging to the environment than lithium ion. But I guess I could be wrong.
On another subject, if I were to add additional battery capacity to my Avalon hybrid, NiMH would be the least hassel, not just because the car is designed to charge NiMH, but because there would be less to do with thermal management and with fire prevention.
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