Turnigy 2S2P Nano-Tech 65-130C issue
 

I have 6 of these batteries which were purchased new about a month ago and they all seem to perform well on the track (used in an HPI Vorza, Hobbywing WP SC8 ESC and 2700kv motor) but when charging one of them won't balance.

One cell goes slightly above 4.20v and one remains slightly below. According to the charger (Core RC UAC-50 which has never given me any real trouble) the cells are 4.23v and 4.18v, I have a Skytronic (chinese) multimeter that measures them at the same voltages but my Draper multimeter that i've had for years says they're 4.18v and 4.11v respectively (all these measurements are when the charger has been sitting at 0.1-0.2amps trying to balance the pack for 15-20 minutes, i.e at the end of a balance charge).

I must say out of the 3 devices used to measure the cell voltages, i'm inclined to believe the Draper multimeter. The pack isn't getting hot when the dominant cell reads more than 4.20v, all that happens is the charger won't finish charging like it does with all the other packs (although I have a couple of these UAC50s and they are a bit sensitive when balance charging, sometimes they take longer than others).

Does anyone have any suggestions? As I say I can't detect any performance difference in use between this pack and the others so could it be that a difference between cell voltages of 0.05-0.07v is not really a problem, even with a brand new battery?

In my limited experience I have found most charges seem to have a margin of error built in and will never charge a battery to actual 8.4v

If a pack is slowly going further and further out of balance you could find it takes up to an hour or more to balance. If you are balancing out .05 of a volt that is likely to be a few hundred mah, chargers balance at like .1 amp so it's not unreasonable to think it will take a while.

If it where me, I'd leave them on balance and monitor them every 10 mins just for peace of mind.

And remember to always charge in an approved lipo sack.

Thanks, someone on another forum has said exactly the same as you about this so +1 to everything you've written (especially the LiPo sack), will try this next time I charge the pack:).

Have you tried recharging them as 2 single packs instead of a pair (if you have a lead that can do that) so that they are both equal then if your charger has the function of putting them as a pair into storage mode.

Leave a couple of days then try and balance chareg them again and see if they equalise.

Other thing to try is charging them at about 50% rate your would normally use and see if that helps

That sounds like a good idea, it wouldn't be much aggro to make up a lead and then I can treat each cell in the pack as a 1S and see if that helps. Thanks!!

Clean the balance connectors. I have had this problem before on many lipos over the years and just recently found out that cleaning the connector contacts inside the balance plug woulda saved me 100s of dollars in thrown away batteries I thought were bad cells.

Use non conductive electrical contact cleaner and find something thin and small you can insert into the connecter, not too big or it will stretch the contacts in there.

If you can't find anything, get a set of male balance pins, scratch small horizontal lines on the pins so they act like a file when you connect them in the lipo's female connectors. Spray the electrical cleaner inside the holes of the lipo's bal connectors and then take the male connector and connect disconnect rapidly. Rinse and repeat about 3 times. each time you spray cleaner in there you may see black crap flow out, keep doing till that stops.

Thanks Jason, my balance charging leads are about a year old so this is also worth doing. They're only small terminals and it wouldn't take much corrosion in there to build up some resistance:)