I have had lots of people ask me to send them an 1800 or 3000 mah battery pack. When I ask them what they plan to charge it with, some of them say "The wall charger that came with my radio"

Unfortunately, I don't get to talk to everyone who buys a big pack, so I'll explain something here.

If you try to charge an 1800 mah pack with a wall charger that puts out 60 mah, you will never get the battery fully charged no matter how long you leave it plugged in. A charger must put out at least one tenth of the capacity of the battery in order to achieve a full charge in 16 hours. In the case of an 1800 mah pack, that would be 180 milliamps.

After only an hour on charge, the no load voltage will read 5.0 or higher. That doesn't mean the battery is charged!



Why is it so important to check your battery with a load?

The graph below shows 4 tests run with the CBA II

Test #1, the Black line, is a normal test on an old, fully charged 4 cell NiCd pack under a 2.5 amp load. This was a pack made up of balanced cells.You can see the disadvantage of using balanced cells by noticing that when one cell goes, they all go. This is why the last couple minutes are practically vertical. A normal pack would have a little less vertical drop-off.

Ok. So now I have a battery that has been completely discharged, but I noticed that the no load voltage had climbed back up to 4.94 volts. If this pack were in my helicopter and if I tested it without a load, it would read 4.94 volts. That's plenty to fly, right? Wrong!

I started another test without charging.

Test #2, the Green line, started out at 4.9 volts and I used a 1 amp load.
Test #3, The Red line, started at 4.8 volts and I used a 0.5 amp load.

Tests 2 and 3 would probably simulate a range of actual load while flying. So I thought about what would really happen if I checked the voltage on the bench without a load, decided I had enough and started up. That brings us to:

Test #4, The Blue line shows a 300 milliamp load. The voltage had actually risen to 5.0 volts by the time I started this test.even though it immediately dropped to 4.75 when I started the test.  Had I tested the voltage without a load, I would have had 5.0 volts. Then, I would have started the model up, carried it to the flight line and taken off. I would have had just about enough time to climb out before the pack completely died.

Checking this same pack using a Futaba Battery Checker with a 1 amp load for only two  seconds gave me a voltage of 3.3 volts....completely dead. That's actually beyond dead. It's dead and buried. But with no load it stayed above 3.6 volts long enough for me to get my model started and walk to the flight line.

A model at rest, with no servo activity draws very little current. Had I wiggled the sticks a little bit, the battery probably would have died. That's another reason for you to set your fail safe to idle on the throttle. Hopefully it would have enough voltage left before it took it's last dying breath to move the servo to idle before it totally died.


Three products that work

Futaba Battery Checker

Hanger Nine Digital Voltmeter w/load

Voltmagic. This device tells it all. Click for more details.