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Comment by codeduck | Hacker News Reader

Lithium Iron Phosphate cells can charge at a rate of up to 5C with no side effects - they're used in more expensive hand-tools and as primary power cells for electric radio control aircraft and helicopters.

That said, smartphones don't use these batteries, and anyone who tried to put a couple of amperes into a standard lithium polymer battery is going to have an amusing experience.

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5C is still like 10-15min for a full charge -- and definitely does have side effects, it causes damage to the battery and will result in sagging voltages and lower capacity in just tens of charges. 5C is too high of a charge rate.

I feel like you've mixed up LiFePO4 and LiPo. LiFe has low charge rates, lower energy density, lower voltage, and higher cost compared to LiPo. For R/C aircraft, it's typically used only for the receiver and servos of the really large helis/planes, because its lower voltage is tolerated by the servos whereas a LiPo needs a regulator to step down to 5-6V for driving servos. I can't speak for expensive hand tools, but "everyone" in the R/C community uses LiPo.

No. There are various types of LiFePO4 - some are as you say used for receivers etc but the ones I am specifically referencing (and perhaps should have been more explicit about) are the A123 systems Lithium Iron Nanophosphate batteries, which are capable of 60C burst discharges and 5C charging rates. These are definitely used as primary power-packs for flight - I flew with people who were using them when they first came out.

Sorry. I googled to check before posting too, but didn't consider specifically the A123. It still looks like it is an uncommon choice for main battery pack but I can see how it's at least feasible (I probably wouldn't go for the tradeoff personally).

What exactly do you mean by “5C”?

5 times the nominal rating of the battery - it's a term we throw around loosely in Radio Control, based on Elec.Eng terminology that is too complex for us laymen :) A 1000 milliamp/hour battery has a C rating of 1 i.e. 1 ampere/hour. So for a typical Lithium Polymer you'd charge this at at most 2 Amperes to prevent damage to the battery. A LiFePO4 could be safely charged at 5 Amperes, which drastically reduces the charge time - very useful if you're at a flying site and are charging packs in between flights to extend your flight time and make use of good weather.

ampere/hour

Minor correction: battery capacity is measured in ampere-hour, i.e. ampere * hour.

https://en.wikipedia.org/wiki/Battery_charger#Charge_rate explains it pretty succintly

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