For review I have the Xtar BC8 AA / AAA NIMH & for their proprietary AA / AAA Li-ion battery technology . ( Sent to me by Xtar )
This charger is not a Li-ion charger and you should not attempt to use it as such !
It is designed to recharge NIMH batteries and Xtars own Li-ion AA batteries .
If you keep reading you will see why it could be dangerous to try and use this charger incorrectly !
This charger does not currently show on the Xtar website .
Using the BC8
Honestly , it’s as simple as plugging in the BC8 into a suitable USB power supply capable of at least 5v 2A . To charge NIMH batteries simply pop them into the charger and pull them out when the charger gives a green light ( fully charged ) . The red light signifies the battery is being charged . And this charger is a constant 0.5A charger , so charging is neither fast nor slow . In fact the charger is nice and easy on the batteries and I did not detect any over heating on the AA or AAA I charged . AA stayed in the 30 deg C range and I did see 42C on a few AA , ( Room temp was 20 deg C ) .
A unique feature of the BC8 is the hole in the back of the charger . I believe this is to aid in the extraction of batteries that have completed their charge cycle . It can be a real pain peeling the odd battery out of a charger once it has finished charging and the hole in the back allows you to simply push out the completed battery with little effort .
Charging AA / AAA LI-ion ( From Xtar )
Just as easy as charging NIMH batteries . Just pop them in the charger and he charger automatically detects them and charges them . Speaking off !
The charger starts at 4.2 volts 0.5A and voltage slowly increases to 4.8 volts and then the current slowly decreases and the charge cycle completes at around 5 volts . This is why it would be a very bad idea to try and charge other batteries ( Li-ion / Lipo ) with this charger .
Video shows the charge cycle for the Li-ion AA … ( Less than a minute = Compressed )
Conclusion :
I had absolutely no issues what so ever with the BC8 charger . All the NIMH batteries terminated as they should , there was no overheating of the batteries or charger that I could detect . In fact it just did what it’s supposed to do with the NIMH and Li-ion batteries ( Xtar ) .
Xtar Li-ion AA / AAA
I ran a discharge at 0.2A on one of the AA Li-ion batteries .
Initially the voltage dropped slowly into the 1.2 volt range ( being discharged )
The voltage bottomed out at 1.14 volts around 1000mAh having being discharged and then began to rise !
1359mAh / 1.17 volts
1477mAh / 1.23 volts
1485mAh / 1.3 volts
1514mAh / 1.32 volts
1604mAh / 1.32 volts
1745mAh / 1.32 volts
1814mAh / 1.32 volts
1915mAh / 1.32 volts Terminated Discharge .
So the way the AA Li-ion work is … There is a li-ion battery inside with a driver that regulates voltage ( 1.5v ) .
I did run a discharge against a NIMH at one Amp discharge … To see which battery could deliver better voltage under load ( being 1 Amp )
Nimh battery at 1 Amp discharge = 0.76 volts
Xtar Li-ion battery at 1A discharge was 0.88 volts
It’s a small difference , but the difference favors Xtars Li-ion AA .
I have the same charger and cells. How in the world do you measure voltage on these 1.5v li-ion AA cells? When depleted, my multimeter will still read 1.5v. Or are you somehow able to measure voltage actively during discharge (how do you do that)?
Thank you for confirming that the charger terminates NiMH properly. IIRC, I contacted XTAR and they also told me that the BC8 does not trickle charge NiMH after finishing the main charge cycle.
A) There is a li-ion inside with a driver that reduces voltage to 1.5v …
B) I can measure voltage because I use a hobby charger discharger to discharge … … Simple … It gives a constant read out on the battery voltage .
Also good if you want to see / test voltage sag under load .
Since I fly RC ( electric ) I own 3 Lipo / Li-ion etc hobby chargers for RC related batteries . ( and other batteries )
One of them can discharge up to 5A … If you need to test li-ion hard … I have had several cheap 18650 voltage collapse at 3A current draw …
I even had one voltage collapse at 2A … And when a battery voltage collapses in a multi battery situation , FUBAR happens … Like reverse polarity / shorting …
Voltage sag :
Under load , the battery will drop voltage … The higher the load , the more the voltage will drop to maintain that load ( call it stress )
Voltage collapse :
Under load voltage drops … Some batteries will completely fail when the load gets too high and give a 0 voltage reading or near zero volts …
This is bad ju ju as this situation can cause a short or reverse polarity situation .
I agree with @radellaf.
What NiMh and what kind of condition? Voltage drop to 0.76V @1A is lousy. I expect better out of any reasonable AAA NiMh.
Voltage sag on 1.5v Lion-NiMh to 1.14v @0.2A is also lousy. I’ve got a number of 1.5v Lion and generally they can sustain at least up to 0.6A and maintain 1.4v+. After that some heat up and have trouble. Some do a bit better. They SHOULD maintain close to 1.5v voltage under load or they simply aren’t worth buying at all as they don’t live up to advertised spec.
Are you sure this is not an artifact of your hobby charger discharge reading?
I think part of the behavior is the driver …
And the other part is how you interpret the information …
I ran a discharge at 0.2A on one of the AA Li-ion batteries . Initially the voltage dropped slowly into the 1.2 volt range ( being discharged ) The voltage bottomed out at 1.14 volts around 1000mAh having being discharged and then began to rise !
1359mAh / 1.17 volts
1477mAh / 1.23 volts
1485mAh / 1.3 volts
1514mAh / 1.32 volts
1604mAh / 1.32 volts
1745mAh / 1.32 volts
1814mAh / 1.32 volts
1915mAh / 1.32 volts Terminated Discharge .
So these listed readings are from when the voltage began to rise … ( Buck N Boost ? )
A) For capacity
B) To get some idea of the driver behavior
As for 1A discharge and voltage drop … If mem serves it was an Eneloop … ( I did this some time ago )
And I don’t remember how many AA I tested for voltage sag .
What ever , just think of it as a direct comparison between batteries under my Discharge conditions .
Which might not be comparable to your test conditions / equipment …
If anyone wants to : Might make for a great Battery test !
Go out , buy some various brand AA and then do some voltage sag under load testing and post the results …
