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I'm planning on building an Ebike and I am not quite sure what type of battery I should get.

What are the bigger differences between the two?

I have Googled, but I don't understand the answers.

I don't care about weight and size, just efficiency, power and safety.

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  • \$\begingroup\$ Without knowing your power and energy requirements answering your question is pretty difficult. \$\endgroup\$ – Vladimir Cravero May 23 '15 at 16:02
  • \$\begingroup\$ @VladimirCravero Just asking general differences between the 2 technologies \$\endgroup\$ – Arbitur May 23 '15 at 16:48
  • \$\begingroup\$ My understanding is that the LiFePO4 is somewhat safer and can be charged and discharged faster without creating an unreasonable safety hazard. If you look at how much energy they store, compared to weight, the LiFePO4 is not quite as good as lithium ion/lithium polymer cells. My feeling is that the LiFePO4 is the better choice for a bicycle because of its ability to tolerate very rapid discharge. \$\endgroup\$ – mkeith May 23 '15 at 17:27
  • \$\begingroup\$ Does “power” mean power density or power output rate in your case? \$\endgroup\$ – neverMind9 Oct 25 '18 at 22:36
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Lipos have higher voltage per cell (3.7 vs 3.2). All else being equal this equates to more power. Lipos may also have lower internal resistance and higher maximum discharge rates, which equates to even more power.

If you want to make a fair comparison then weight and size must also be taken into account. Lipos are generally lighter and more compact than LiFes. This means that for the same amount of battery you will get more power and longer run time with Lipos.

Both type have high efficiency (ratio of energy output to input) when charged and discharged at moderate rates.

The main advantage of Life is safety. Lipos begin self heating at temperatures as low as 60°c, and once the interior starts to burn the whole battery rapidly 'explodes' into flames, setting fire to anything nearby. LiFe is more resistant to thermal runaway, 'cooks off' at higher temperature, and burns much less energetically.

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    \$\begingroup\$ I read also that when the capacity drops the LiFe voltage doesnt change as much as LiPo is that correct? \$\endgroup\$ – Arbitur May 23 '15 at 19:57
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    \$\begingroup\$ Yes, Life generally has a flatter discharge curve. This means it may provide more constant power over most of the discharge, but also makes it harder to tell how much capacity the battery has left. \$\endgroup\$ – Bruce Abbott May 24 '15 at 3:55
  • \$\begingroup\$ So you would calculate the remaining capacity (V/3.7)*mAh ? \$\endgroup\$ – Arbitur May 24 '15 at 10:55
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    \$\begingroup\$ Lipo resting voltage: 4.2V = 100%, 3.85V = 50%, 3.7V = 10% capacity remaining. \$\endgroup\$ – Bruce Abbott May 24 '15 at 11:06
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    \$\begingroup\$ 3.7V is just the 'nominal' voltage that was chosen for Lipos (based on average discharge voltage under load). The actual voltage is determined by the particular chemical makeup of the cell. Modern cells have improved chemistry that maintains higher average voltage, but manufacturers continue to rate them at 3.7V nominal because maximum and minimum voltages haven't changed so they can use the same charging circuitry. \$\endgroup\$ – Bruce Abbott May 24 '15 at 21:35

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