Weird relative capacity question the Li-Ion vs the Li-Fe-po

[VidPro]

I wondered about this a few times, and now i toss it up for discussion.

There are some lights that go into overdrive when using a battery voltage over the VF of the led, or about 3.7-3.8v.
[Single battery, boost curcuit, single white led.]
Lights designed for the 3.0v Primary Lithium.
But Primary batteries go in the trash :scowl: and in the small stuff , they go in the trash to often, rechargables are King!.:thumbsup:

These lights would "survive" if the voltage stayed below say ~3.9V charged, as there is various resistances in the flashlight components anyways.

Now, they have the Li-Fe-po, which is lower voltage. you could say its the "correct" voltage, for keeping an overdrive from occuring. A Li-Fe type of cell can usually replace a Primary (3v) type without destroying/overdriving the lights. But Li-Fe-po has terrible total capacity right now.

Quick summary:
Li-Ion goes over spec for lots of lights expecting a primary 3.0 cell.
Li-Ion has good capacity , not as great as a primary, but its reusable.
Li-Fe-Po , is TERRIBLE total capacity :-( although its closer to the max voltage.

Finnaly the Question:
Whats the real difference if you 1/2 charge a Li-Ion, Vrses using a li-fe-po that has no capacity anyway?

for example: charge a Li-Fe-po to 3.8v and charge a Li-iIon to 3.9v and which one would still Last longer?
which one would charge up faster then?

So other than some safety issue, wouldnt a Li-Ion less charged, be a "better battery" than a Li-Fe-po Fully charged?

 

[SilverFox]

Hello VidPro,

You still have to deal with the nominal voltage of the two chemistries. Li-Ion chemistry runs around 3.7 volts and LiFe runs around 3.3 volts.

Capacity wise, a Li-Ion cell charged to 3.9 volts is at around 65% of its total capacity, so both chemistries would yield around the same capacity, but the Li-Ion cell would do it at a higher voltage.

Tom