Efficiency of different battery types

I've been looking into the wealth of small rechargeable batteries lately, more precisely li ion types (lithium iron phosphate and lithium ion polymer) and there are tons of battery charger ICs on the market which all try to compete with each other in efficiency just like we're used from buck or boost converter manufacturers.

However I find surprisingly little info on the battery efficiency itself, i.e. if the charger pumps 100 J into a battery at a capacity of around 50%, how many joules can you get out again? Since batteries heat up during charge and discharge, it's obvious that a certain amount of energy is lost by storing it into the battery and recovering it again, but how much? Why do manufacturers not mention this in datasheets?

If someone could point me to relevant literature I would be most thankful!

A Lithium rechargeable battery is VERY efficient if you do not fast charge it with a very high current and do not discharge it at a very high current.

Rechargeable batteries are preferred not for their real efficiency but for the capability to deliver a high output current when needed.
Manufacturers do not specify this efficiency, also due to the fact it is temperature-dependent and widely variable under various conditions.
Lead-acid batteries can be ~20-30% efficient but worse in cold, modern Lithium and other types can achieve almost 50% but again lower when cold (some must be heated to operate), and they are quite sensitive to charging voltage and current.

Audioguru said:

A Lithium rechargeable battery is VERY efficient if you do not fast charge it with a very high current and do not discharge it at a very high current.

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jiripolivka said:

(...) modern Lithium and other types can achieve almost 50% but again lower when cold (...)

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It appears to me that those 2 statements are contradicting each other... or at least, 50% is not what I would call VERY efficient. Audioguru, could you elaborate your statement with a quantitative example of order of efficiency you have in mind?

ArticCynda said:

It appears to me that those 2 statements are contradicting each other... or at least, 50% is not what I would call VERY efficient. Audioguru, could you elaborate your statement with a quantitative example of order of efficiency you have in mind?

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I use many Li-Po batteries to power my radio controlled model airplanes. They charge at their mAh rating and do not even get warm so their charging is very efficient. If their discharge current is reasonable (up to 10 times their mAh rating) then they again do not get warm so their discharging is also very efficient.

I think Jiripolivka said their efficiency is 50% because a linear charging circuit wastes a lot of power getting hot. So use a switching charging circuit that does not get hot then the charging efficiency of the charger will be high.

Audioguru said:

They charge at their mAh rating and do not even get warm so their charging is very efficient. If their discharge current is reasonable (up to 10 times their mAh rating) then they again do not get warm so their discharging is also very efficient.

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That is also my experience with Li iron phosphate and Li ion polymer batteries, but I am looking for hard evidence and efficiency percentages, which appear to be hard to find.

There's a wide variation of LiPo technology with variations in cost, lifetime, ESR, C rates and hence efficiency vs C rate.

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98% is typical for efficiency. at slow rates.