An absolute must for any electric model flier.
Having a Battery Voltage Display in your toolkit will make looking after your batteries easy.
Simply plug the unit into the balance connector of your LiPo battery and it will display each individual cells voltage as well as the total pack voltage.
This device comes in handy at the field and at home.
At the field, plug the device in after you've finished your flight to see how much power you have left. You may find you have another couple of minutes up your sleeve.
At home, plug the device in to check the voltage of your batteries if they have been left a while. The voltage may have decayed indicating the battery may need a top up charge to sit at 3.8V per cell (ideal storage voltage). Or maybe you have a few similar battery packs and you cant remember which one you have charged/discharged. Plug in the unit to get an immediate display and cut out the guess work.
This unit is also handy for those who have a charger that does not display information about the charging process. Plug in the unit after the charge is complete to help verify that the battery is indeed charged.
Here's a rough guide to LiPo battery cell voltage and it's relationship to charge level.
3.0V per cell - 0% - Completely flat, NEVER run your LiPo's this low if you want them to last. Batteries left sitting at this level will self-discharge and may not be recoverable. In other words, it's dead and there's no way to bring it back to life.
3.6V-3.7V per cell - ~20% - This is considered by most to be the ideal stopping point. Batteries that are discharged further on a frequent basis risk damage to the cells. A small amount past this is on an infrequent basis is usually tolerated by the cells and should not have any lasting effects.
3.8V-3.85V per cell - ~50% - The ideal voltage for storing your LiPo packs. At the end of each flying session make sure your packs are within this range for optimum lifespan and power output. Most packs don't mind spending a few days up around 3.9V per cell, but this is still discouraged. Packs stored higher than 3.9V per cell risk damage to the cells in as little as 4 weeks.
4.2V per cell - 100% - Fully charged and ready for action. Try not to leave your batteries at this level of charge any longer than you have to. Packs left sitting at 4.2V per cell risk damage in as little as 48 hours! Although the damage is only minor at the 48 hour mark, periods of time exceeding this will leave a permanent scar. A LiPo left or kept fully charged will be very noticeably weaker in its discharge performance. i.e Your model will lack power and your flight times will be shorter.
So in short, don't leave them flat, don't leave them full. 3.8V per cell is where you want to keep your batteries for a long and happy life.