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What is the difference in self discharge rate between lithium iron phosphate battery and lithium polymer battery?

I have a remote application in which the self discharge rate matters a lot.

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  • \$\begingroup\$ Datasheets should have that information. No datasheets? \$\endgroup\$ – JYelton Oct 1 '14 at 20:00
  • \$\begingroup\$ yeah, thats the problem. My vendor doesnt provide datasheets. So im just going for the general knowledge here. Is it not possible/ difficult/too close to generalise? \$\endgroup\$ – Denis Oct 3 '14 at 0:53
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You can look at similar parts' datasheets and white papers to get an indication of the typical self-discharge rates for the style of LiPo and LiFePO4 cells you are considering. Typically, both the LiPoly and LiFePO4 types have self-discharge rates roughly less than 5%/month when stored under ideal temperature and state-of-charge conditions. With the limited amount of infomation on the particular parts you are asking about, it is not possible to find the difference between the two chemistries with respect to self-discharge.

One more thing to consider is that things like self-discharge can be quite variable, depending on how well the manufacturer can maintain a cell-to-cell and lot-to-lot consistency in the process. Even with this, the conditions that your device will be subjected to may cause a cell to change, and you will either want to design to mitigate these conditions or factor in some allowance for capacity dropping over time, and self-discharge increasing.

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Probably you already have found that LiFePO4 are costly than Li Polymer. If both attends your specification of capacity I recommend go with LiFePO4 if weight is a important factor. If not, buy the cheaper. For better autonomy, avoid regulators. Try to use the voltage supplied by the battery directly. If it's not possible, never use linear ones but switched ones (take a look at buck converter). Also, take a look at some ways to auto charge your batteries, like solar panels (they are cheap if you are not handling with big loads).

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    \$\begingroup\$ Also, when handling with lithium batteries, always remember to design a protection circuit to prevent against short-circuit, overcharge and undercharge (if possible do it for each battery and cell). The first and second ones you can prevent being careful when charging and mounting your circuit. The third one deserves special attention, since probably you will not measure the voltage on batteries frequently. \$\endgroup\$ – Pedro Quadros Mar 17 '15 at 19:15
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I have a motorcycle battery that is made up of eight A123 ANR26650M1A LiFePO4 cells in 4S2P configuration. I was wondering about self-discharge and made some measurements with it connected/drawing about 2 mA and disconnected. The pack was somewhere around 60% charged. Voltage measurements were made on a daily basis. The A123 specs indicate that in the range where measurements were made, a drop of .02 V in the pack voltage is about 3% of charge capacity. The results were:

Connected: 13.404, 13.396, 13.388, 13.384, 13.379, 13.374, 13.371, 13.368

Disconnected: 13.368, 13.373, 13.374, 13.374, 13.374, 13.375, 13.375, 13.375, 13.375

I'm guessing that the rise when first disconnected had something to do with being disconnected. After that the voltage was very stable. The 1 mV increase in mid-test may be associated with a heat wave that arrived during the test period and could be either the battery or my meter. Things were so stable that I could only estimate that the self-discharge rate was no more than 6%/year. To get a better estimate I'd have to make these measurements over several months and I wasn't interested in waiting that long.

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Generally the self-discharge factor is used when the battery is stored for long periods of time. Therefore, the SOC (State of charge) at which you store your battery will mainly determine the self-discharge rate of your battery, due to the OCP (Open circuit potential) at which the battery is at that specific SOC. The higher the OCP of the battery the higher the self-discharge rate.

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