Battery Maintenance Tips from Emails
Below are a couple of clippings from people on the IMAC list that bring up some excellent points about maintaining battery packs - especially on giant scale planes.
You can tell how much your system uses by first charging the pack, then discharging and recording the capacity delivered. Then charge fully again, go flying and record the exact minutes that the system was on. Immediately upon returning home discharge the pack and see how much capacity remains. The difference between what you got on the first discharge and what you get after flying is the mAh used. This divided by the time you flew gives you the mAh/minute of flight. Using a watch alone (assuming you fully charged the pack before you go flying) will tell you just how much flying time you have left. leave yourself a good margin of safety, like 20% or more.
Red's R/C Battery Clinic
The fact is everybody's' circumstances are different. Everyone's' discharge rates are going to be different. With a fully charged pack you would go to the field, fly one flight of regular duration, land and measure the voltage. The next flight, do the very same thing and note the voltage when you land. The difference between these two voltages is representative of the voltage drop/current used for that flight. After a number of flights you will begin to see that a certain amount of power has been consumed for a given length/style of flight. Depending on the rate of discharge will dictate your lower limit i.e.; A small pack used in a large A/C ( to optimize weight for example) will consume said pack sooner than if a larger, higher mA rated pack would. This would require you to charge at the field to get a good days flying in, which is not a problem. If I recall Sanyo rates there cells at 500+ charge/discharge cycles. Under "normal conditions" (charge @ 0.1C X 11 hrs, discharge @ 0.7C X 1hr) after 1000 cycles one might expect to lose 20% of capacity.
Instead of cycling every other day (notice, loss of capacity) do it every couple of months. Look for changes in the longer time scale. When you check loaded V at the field look for short term changes such as depressed/reversed/dead cell(s). I have had a cell die while airborne (I use 5-cells exclusively) and I became immediately aware of the response rate. I landed and discovered the problem.
BTW, most of my comments although apply generally, are geared towards larger A/C and their associated flight loads.
From: Simon Van Leeuwen