Hey folks

Ive got a spektrum 8010 receiver 2 switches and 2 batteries, 1 is inserted into the bat port the other is on a spare port. when i charge the batteries at the same time i allways get more mah in the battery in the bat port than the one in the spare port. batteries are life and are the same age and both have low resistance. is this normal?

What is the capacity of the batteries and what is the spread. Have you switched the ports to confirm its battery and not the port being used?

+1 on Festivus

Originally Posted by Festivus

What is the capacity of the batteries and what is the spread. Have you switched the ports to confirm its battery and not the port being used?

2200 mah and im not charging through the switch its about an 80 or so mah difference

I personally wouldn't worry too much about an 80 mAh difference. I have a 2s life, even the 2 cells within them are out of balance after a discharge and one cell always takes more.

It could be just the difference in calibration of the two Chargers next time you fly charge both batteries back with the same charger and see if there is a difference I usually get within about 15 to 20 milliamp on each of the Dual batteries I run 5200 milliamp lipo 2 s using a charger 360b on a balance board

And it also may just be the finite difference between two batteries from the same manufacturer 80 milliamps does not seem drastic to me but there are many many people on here who hopefully will provide an answer that know far more about batteries than I do

Originally Posted by tazx100

2200 mah and im not charging through the switch its about an 80 or so mah difference

Are you disconnecting the batteries from the rx when you charge?

You should never charge two batteries with two different chargers while still connected to the rx.

The reason is that almost all of our chargers use "low side sense" to read battery voltage and that is basically the ground side of things. So if you do not disconnect the rx, the chargers can read voltage off the negative side of both batteries at the same time. That is NOT a good idea.....

Originally Posted by Zeeb

Are you disconnecting the batteries from the rx when you charge?

You should never charge two batteries with two different chargers while still connected to the rx.

The reason is that almost all of our chargers use "low side sense" to read battery voltage and that is basically the ground side of things. So if you do not disconnect the rx, the chargers can read voltage off the negative side of both batteries at the same time. That is NOT a good idea.....

I have a hitec charger that charges 2 batteries at the same time, I have one lead for each battery that i charge through, I figured this was a common event but then again I am not a battery guy. Not arguing but this is the first time I heard you should un plug the leads from the rx, I ve never checked if there is any currrent in those lines when charging either.

I run dual A123s in direct parallel on a number of planes. They never recharge exact the same, small differences in IR, or the length of the wiring can do that.


If the difference is big (hundreds of mAh) I might be concerned, for your issue I would not worry.

Originally Posted by tazx100

I have a hitec charger that charges 2 batteries at the same time, I have one lead for each battery that i charge through, I figured this was a common event but then again I am not a battery guy. Not arguing but this is the first time I heard you should un plug the leads from the rx, I ve never checked if there is any currrent in those lines when charging either.

As I said, if the batteries are still connected to the rx, there is a common ground between them through the rx buss.

Try this link to a search I did for you over on RCGroups which has a much larger data base of all sorts of categories than what FG does. Lots of info on more than common ground issues in this search, you can learn a lot if you choose to do so.

https://www.rcgroups.com/forums/sear...mmon*ground%22

Originally Posted by Zeeb

Are you disconnecting the batteries from the rx when you charge?

You should never charge two batteries with two different chargers while still connected to the rx.

The reason is that almost all of our chargers use "low side sense" to read battery voltage and that is basically the ground side of things. So if you do not disconnect the rx, the chargers can read voltage off the negative side of both batteries at the same time. That is NOT a good idea.....

You are mistaking voltage and current. “Low side sense” is a technique for measuring current flow (Amps) through the negative terminal.

Voltage is the potential difference between 2 points of a circuit. To read the voltage of a battery, the charger or multimeter HAS to connect to both positive and negative leads of the battery being tested.. Reading a voltage only from probing the negative side of the battery is impossible.

Unless the switches where left on, the positive leads of both batteries should be disconnected when he is charging. Even if the switches are wired to leave the negatives connected when off (a common ground) this can’t cause a voltage reading error. .. now if the batteries where charging simultaneously on 2 different chargers powered by 2 different sources and there was a source side ground potential difference you could get a ground loop and have current flow between the chargers ( not good) but I kinda doubt that’s the issue here as other bad things would be happening

With a Powersafe rx, it “ping pongs” between the batteries and draws from the higher voltage battery. Last week after 4 flights the 2 batteries were within .01 volts of each other.

When I use 2 batteries 2 switches, I also use the smart fly batt share. It helps keeps the batteries even and if one shorts, it pops a diode to keep the other from shorting