Not flying for a week - leave lipo discharged, storage or fully charged?

[muscleflex]

thanks. is this a good one? i only need 3 cell capability for the time being as i only have the 450 helis.
no plans of getting a bigger heli anytime soon.
will i need a power supply with this charger or is this from the mains?

This is the one. Available for around £30. Most chargers will do the same. They just need a capacity or time limit.

http://www.astecmodels.co.uk/pdfs/Imax-B5%20manual.pdf


Ripmax O-SKYCHB5 - Sky RC Imax B5 Charger


Chris

[moyesboy]

THe main thing is not to let fully charged packs get cold (less than 10 degrees c) as the capacity gets less and they bevome overcharged.

This is the first I've heard of fully charged lipos suffering from the heat.

I always keep my packs fully charged, and sometimes they are in hot places.
I don't let then get cold in the winter.

Some of may 5S4200 revolectrix are almost 3 years old and still going strong (but they don't get that many cycles, becuase somehow I ened up with 8 of them, mostly second hand).

[bikerflier]

I mark each battery after every charge to try to get an understanding of useage and life.
I used to charge after every flight so they were ready for next time. This means that the batteries were effectively fully charged throughout their life. I changed to leaving them discharged at 3.8v until next needed and I have seen a dramatic improvement in them. performance degrades less over time, so they still have the same sort of 'grunt' as when new for longer and the overall life span has considerably increased.
I really do believe, and have proven it to myself, that keeping batteries at storage 3.8 volts until needed is the right way for good life and performance.
We're careful to avoid spilling fuel so why not take that extra care to not spill the life out of our batteries.

Many good points raised by cjcj1949 and worth noting.

It's a cumulative effect. The higher the temperature and the higher the voltage the more the pack degrades. The lower the storage temperature down to fridge level the better and the lower the volts. The only limit on how low to keep them is that the volts will drop on discharge and if it drops too far (below 3V) then the pack can be damaged. It depends how long you want your packs to last and if you keep them in a hot car. I keep mine between 3.8 and 3.9V when not in use. Mine last a lot longer now. Record is 18 months. If you leave them for a week it could turn into a month. You can keep one fully charged for immediate emergency use and put the others on charge before you start flying. It is a matter of opinion though as it takes a while to get results.

Chris

[cjcj1949]

I'm just the messenger. I took some convincing from someone whose lipos lasted a long time. I wish it wasn't true as it is a real pain. It may of course only be true for old lipos and not new ones. Also better quality lipos like the revoelectric probably last longer. I haven't seen any evidence about batteries being overcharged when they get colder. The battery voltage doesn't seem to change much with temperature. Not as much as the internal resistance anyway. You can see that change if you just hold a pack in your hand. One thing I have noticed this Summer is that I can get longer flights about 20% I think.From about 5mins to 7mins. Even though I warm the packs up in the Winter. Other people (Vicp I think) have suggested running the packs slowly for a minute in the cold to get them warmed up. can confirm that this does make the internal resistance drop and possibly prevent damage caused by more localised heating. Lipos are getting better all the time though, so hopefully in the future we'll be able to treat them more like NiCds and just use them. The next one that fails will get replaced with a 60C Overtec.

Chris