I have a decision to make regarding an upgrade of a lighting system. If you were road cyclist who occasionally wanted to ride a 24 hour ride or ride all night what would would be your choice for a battery supply source? Assume for the sake of the poll that one set of Lithium Ion batteries could last all night, but NiMh batteries would have to be replaced several times.

Extra comments regarding comparison appreciated.

Today, LiIon without a doubt. You can HAVE my old NiMH battery.

For tomorrow, none of the above.

Lithium iron phosphate (LiFePO4). They're a bit hard to find now and a little expensive, but I think they'll get more common. They're already the hacker's choice on eBikes and are used by some high end power tools.

Very high capacity, very long life, almost impossible to abuse to death. Not as subject to runaway overheating / outgassing (fires). Also, non-toxic (LiIon are toxic) and eventually may be cheaper.

Li ion and Li polymer cells certainly have much higher energy density than NiMH. However, I still use NiMH (Eneloop), and they serve me well for my hour long night time commutes. I'm just nervous about the tendency that Li batteries have for "venting with flame". I know that many use Li batteries with no problem at all. I just don't trust myself not to absent mindedly do something wrong. Also, I worry that Li cells and chargers tend to come from parts of the world that are not known for their quality control. Once LiFePO4 become less expensive I'll probably go with them.