LIPO battery info

Lipos do not like to be too cold or hot when being used.  Ideally they should be 20C/68F to 35C/95F before the flight.  They work best when hot (52C/125F), but they don't last as long (use cycles).  When flying on a winter day it is best to keep the battery for the next flight in a warm place.  A pocket in your inside clothes can be used, but be warned that this could cause severe burns if the battery is shorted out by something metal in the pocket, or if the battery is damaged such as by falling and landing on it.  Research lipo safety and decide for yourself if you are willing to assume this risk.

3.8 volts per cell is "storage voltage".  Store at that voltage every time and they will last longer.  If they sit at full voltage for a year, they are basically bad at that point.  If they sit at full voltage in a hot car for a month they are basically bad at that point.  Charge just before usage.  If you fly every week and charge them fully as soon as you get home, after a year, you have still made them sit at full voltage for a year.

Unused packs should be charged/discharged to storage level and stored in a sealed baggie in your refrigerator if you aren't going to use them (like at end of flying season or extra batteries not currently in use).  After removing from the refrigerator, leave them in the baggie until they have reached room temperature to avoid condensation on the battery.

Batteries show a lower voltage under a flight load then they do when checking them after landing.

If you set your battery alarm voltage a little above the minimum, you get a minute or so to fly back and land.

Well used packs have more voltage drop so you can set the alarm voltage lower.  Newer packs hold the voltage more constant, higher, longer and then drop quickly, so you should set the alarm a little higher.

Some people just time their flights instead of using a voltage alarm, but that doesn't handle the differences of temperature or stunt vs. gentle flight.  With an alarm, you can tell if you are "over amping" (which causes a lower voltage condition) your pack.  If the alarm goes off too soon, under a heavy load, don't hit it so hard, and your battery will last longer.  A pack that is too cold will also alarm when loaded, so warm it up more next time.

The better alarms watch individual cells.  It's better to do that than to watch total voltage.  You can fly a pack with one weak cell in it as long as you don't damage the weak cell further.  3.1+3.7+3.7 looks the same as 3.5+3.5+3.5.  At those voltages you are hurting the 3.1 cell, but not the 3.5 cells.

On typical quadcopters a 3.6v per cell alarm works well.  Land quickly when the alarm goes off.  The resting voltage will be 3.7 to 3.8 volts per cell.  If you fly just a little longer the resting voltage will be more like 3.6.

For old batteries (or very high current applications), using a 3.5v or 3.4v per cell alarm is very comparable in final resting voltage to good batteries with alarm at 3.6v, because of the increased voltage drop under load.

For lower current applications such as fixed wing, you can set the alarm to 3.7v per cell.  The low current means less voltage drop, so when it says 3.7 in flight it is probably 3.8 resting.  A high current application should be set at 3.6 and then the alarm will sound at about the same charge level.

Examine your resting voltage after every flight and adjust these guidelines and your alarm loitering time, so that your lowest resting voltage is never less than 3.6 per cell after a flight.  There isn't much power left after that and 3.7 is much safer.  You probably haven't hurt it, even down to 3.5 resting after a flight, but immediately charge to storage level.

Remember that a multicopter must still be hovered for a little while while you are landing, and that does take some charge.  Fixed wing power can be cut off and glide in with basically no further drain.

At the last flight of the day, land immediately when the alarm goes off and you should have something between 3.7 and 3.8 volts, perfect for storage, otherwise you can get an additional 30 seconds or so and resting voltage will be down to 3.6 or so.  It really isn't worth it to try to get more out of it.  At 3.7v resting you have used about 90% of the pack capacity.  It isn't worth it to try to use more.

Some manufacturers claim 3.3v per cell is as low as you should go.  Some claim 3.0v per cell.  Don't ever let them go below 3.0v per cell under load or 3.3v resting.

If you drain the pack down low for some reason, IMMEDIATELY (within minutes) charge it up to storage voltage.  It can survive a minor deviation once or maybe twice for one minute each time.  You might have hurt one or more cells so expect weak cells to loose power more quickly than before.  If you leave it dead overnight, it has probably been damaged beyond repair.

Only charge at the recommended charge current or less.  If you don't know, assume it is 1C.  1C means 1 times capacity.  If the capacity is 2200mah (milli amp hours) (= 2.2 amp hours) then for 1C you charge at 2200ma = 2.2a and it will take about an hour (actually a little more).  If the capacity is 2200mah and the recommended charge rate is 2C, then you can charge at twice that current, 4400ma or 4.4a and it will take about 1/2 hour to charge.  All 1C (charge rate) batteries take about an hour to charge.

Batteries are also marked for maximum discharge rate.  That is also measured in C's.  Typical generic batteries are 20C discharge.  The maximum current you should draw from a 2200mah 20C battery is 2.2 amps (2200ma) times 20 = 44 amps.  A good rule of thumb for long battery lifetime, is to only use half of the stated discharge rate.

Search eBay for:
8s lipo alarm
and you will find these.  Once in a while you will find a setup where you get an early beep that goes away because of noise on the power lines.

Here are good 2s-8s lipo alarms that watch individual cells $1.13 shipped, but you can buy multiples.

Here is an eBay search for the 2s-8s lipo alarms that watch individual cells

Balance Connector Cables

The name of the standard lipo "balance" connector is JST-XH (beware, some lipos come with different connectors, get your lipos with JST-XH balance connectors for compatibility)

These cables are good for balance connector extensions.  $3.66 for 10 (shipped)

$4.50 for 10 (shipped) if the cheap once sell out (or just search eBay)

Further General Information on RCGroups

Balance Connector Cables