Can someone explain the “C” ratings of a battery pack. I’m looking at 6.6 volt LIFE packs and I see 5C, 10C and 20C ratings. What does this mean and which should I use for an RG-65?
The rate at which the battery can be safely discharged.
Usually expressed as 5 or 10 or 20 times the battery’s milliampre rating. Not a consideration in low drain applications like receivers, but may be a factor with a stalled sail winch. Work out the maximum drain on your sail winch and size accordingly. Lower rated batteries are usually cheaper and may have a longer life. Rating is usually for an continuous load, peak loads of less than a minute or so will be higher. What you are trying to do is keep the battery cool.
An example - 1000MaH rated 5C battery will allow a continuous drain of 5 amps, peak drain may be 50% more. At this discharge rate the battery will be totally flat (ruined) after 20 minutes. Normal good practice is to drain the battery by 80% maximum before recharging. Modern chemistry batteries usually have a flat discharge rate maintaining voltage over most of their discharge, making measurement of capacity difficult. A fully charged LiFe battery will show 7.2 volts for some time. A UBEC or BEC circuit for a electric motor is usually used to cut the voltage down to 6v and to provide cutoff before damaging discharge.
Thanks, but fully charge LIFE is 6.6 volts, 7.4 is for LIPO.
A 2S LiFe will show 7.2v to the receiver and servos straight off charge. Most servos will not take that voltage, some receivers do. Working voltage will fall to 6.6 - 6v and stabilize for most of the time. Minimum voltage before damage is 5.6v.
That means LiFe batteries are actually unusable if you discharge it until it’s totally dead? I’ll stay with NiMH cells in that vase. A microscreamer would help prevent it, but they only make those for LiPo batteries. 
OK…? so what was the finish to this conversation???
@TomoHawk:
doing so, you will ruin every battery.
@Steel_knee:
I have 850 mAh Hyperion LiFes in my RG65. Going for a race, I usually change battery at noon. Recharge is then about 350 mAh (depending on the wind). That means, in principle you can go wth one battery for a whole day. However, for a race I would go on the safe side …
Required C rate is very low.
I am using a Dymond D60 for rudder and a Hyperion DH13-FMB for the sails together with a Multiplex M-Link system. All components are LiPo compatible.
After reading this, I would say that LiFE batteries are not suitable for r/c sailing, unless you have a way to know when to change it.
???
There is no other problem like with any battery …
You cannot afford a breakdown of your RC in any case. Therefore you have to change a battery early enough unless you have a telemetry systems which continuously monitors your battery. If a LiFePo goes down to 3V/cell or even less, you should hurry to change it.
Btw, I recognized that two of my old NiMH batteries where nearly dead after winter time by telemetry only. The receiver reported back the voltage drop under load - which was tremendous. After a careful check I realized that usable capacity had dropped from 800 to about 400 mAh - just enough for half a day, but no longer for a full day …
Having used Lipo’s for 5 years or so, I would disagree and wont use NIMH or NICad ever again. Lipo and Life do take a bit more care and feeding. the reward is much faster charge, lighter weight, more charge cycles between failures (in my experience). I just make sure that I have a good idea of how much power I use per hour, then only run the battery about half way down. I usually size my batteries so a lunch time swap for a whole day of sailing is all that is needed. a simple afternoon sail is easily done with one battery. Even with the extra capacity the batteries are lighter than what I used to use. Charging at 1C allows quick charges for big regattas.
If you are someone who is running NIMH packs dead all the time, then they might not be what you need.