LiPo physics

[clicky]

This might be very old question and references to this forum are more than welcome... But...

I've 'heard' that LiPo batteries are not supposed to be fully charged and not used. If they are to be stored they should be charged to the half of their capacity. What does that mean?

More precisely - what is the period after fully charging them you should use them or 'let the pressure out'? Why? Does anyone know the physics of that process and/or did empirical testing to explain what happens (not why)?

What will happen if I charge all my LiPos on Monday and fly only on Sunday? What would be the effects of not charging them on Saturday and keeping them half charged until then?

There must be some good explanation but I must admit as much as I tried to find the answers how LiPo batteries behave I didn't see much (except some graphs how they react on different discharging currents) studies being done, so... :)

Thanks,
click

[vintage1]

This might be very old question and references to this forum are more than welcome... But...

I've 'heard' that LiPo batteries are not supposed to be fully charged and not used. If they are to be stored they should be charged to the half of their capacity. What does that mean?


That means a restng voltage of around 3.7v per cell. Its supposed to be optial for long term storage, but frankly, most of my packs have lasted well enough in a full charge state. They have died from other causes.


More precisely - what is the period after fully charging them you should use them or 'let the pressure out'? Why? Does anyone know the physics of that process and/or did empirical testing to explain what happens (not why)?

What will happen if I charge all my LiPos on Monday and fly only on Sunday? What would be the effects of not charging them on Saturday and keeping them half charged until then?

There must be some good explanation but I must admit as much as I tried to find the answers how LiPo batteries behave I didn't see much (except some graphs how they react on different discharging currents) studies being done, so... :)

Thanks,
click

The accurate answers to all those questions are probably trade secrets. Unless you are laying your packs up for the winter, just charge when you can and fly when you can. Everyone else does.

[clicky]

The accurate answers to all those questions are probably trade secrets.

It's kind of strange that nobody connected a little home brewed device to measure discharge rate of different (generations) of LiPo batteries. And maybe compare their characteristics after different length of batteries being rested/changed...

Unless you are laying your packs up for the winter, just charge when you can and fly when you can. Everyone else does.

I've been doing it with cheap hexTronic batteries and didn't notice much problems, but I've heard that someone who bought evo battery next to hexTronic noticed significant drop of 'power' (*) after leaving battery for couple of weeks (or more) fully charged (unlike hexTronic ones). Now...

(*) - power is 'something' you feel flying helicopters - probably ability to sustain voltage over certain current, but I think that there is more to it... O: )

[AndyOne]

The permanent degradation of LiPo batteries is dependant on not only the charge state but also on the temperature they are stored under. Storing fully charged batteries may not show any noticeable damage if they are kept cool, however, store them in a warm or hot environment, will make them degrade much quicker.

There are no real trade secrets in basic cobalt technology of Li-Pos (Li-ion) high charge state and temperature both degrade the chemistry of the cell.

Andy.

[clicky]

There are no real trade secrets in basic cobalt technology of Li-Pos (Li-ion) high charge state and temperature both degrade the chemistry of the cell.

Andy.


Charging them on the room temperature and storing them in the fridge? Or is it other way round?

[AndyOne]

Charging them on the room temperature and storing them in the fridge? Or is it other way round?

It would be correct to charge at room temperature and store in the fridge.

Charging at low temperature isn't very effective as the cells look more like resistors the an electrochemical system and won't accumulate charge efficiently.

Storing fully charged batteries at low temperature will help to preserve their cycle life as the degradation is a chemical reaction, all chemical reactions slow with lowering temperature. It's a good idea to let them warm up before using them to get the best discharge rate performance.

Andy.

[ccdengr]

what is the period after fully charging them you should use them or 'let the pressure out'? Why?
http://www.batteryuniversity.com/partone-19.htm may shed some light on this. Fully charged storage for a few days is probably not going to make a big difference.