can you charge a lipo and let it sit around overnight and use it? what i mean is do they lose there charge after a while and should i charge it back up if it sits for too long. thanks.

I charge the night before and do not see a huge voltage drop the next day so IMHO you are good to go.
Also if I am not going to be using that pack in the next week or so I store them with a storage charge of ~3.7v per cell

hope this helps
Steve

in balence mode on my charger it charges it to 8.4 volts? i thought it was a 7.4 volt pack? what is a save voltage to stop using it? like 6 volts?

Unlike NIMH, LiPo have very low self-discharge, you can charge it a few days before using it and it won't have have lost more than a few percent charge.

You want to avoid storing it fully charged or fully discharged though. If you are going to store it for more than a few weeks, discharge the pack to around 40% charge. They degrade over time and it's roughly 4% permanent capacity loss per year (if stored properly) but as high as 20% permanent capacity loss per year if stored fully charged.

what if i run it down to where my esc cuts off to save the battery then i put in in my room for a week then go to charge it will it have droped below the safe line of what? or if i run it through my truck then store it is that the way you are supposed to store them?

a lipo packs nominal voltage is 3.7 volts.. they are fully charged at 4.2 volts per cell... your balance charger will stop charging each cell at that number and give a total of 8.4 volts... You are not overcharging them at this point... more than that will be an issue...

I occasionally let my batteries sit for a couple of weeks between full charging and running... I have alot of batteries and don't always run them all.. they at the worst have gone down to 4.15-4.17 volts.. they don't drop like NiMh or Nicd packs... If storing for a long period.. all winter then as Pinolelst said, drop them to 3.7 volts... or 80 %... One or two weeks is not a long time between runs and it won't hurt anything if you do other than add extra cycles to the batteries...

It'll depend on the ending voltage. If it winds up too low at the end of the run it will still be too low when pulled back from storage. It will not drop an appreciable amount from long storage regardless of the resting voltage. If the run was ended at a perfect storage voltage then it will remain that way for a very long time.

When the run is over, the voltage will quickly spring back up to it's true resting voltage , then very very slowly seld discharge. The self-discharge rate is so low that it is insignificant for time periods of less than a month. Even a year is not very significant when talking about healthy lipo seof-discharge rates.