[Update on April 4, 2012]
My original review was written back in August 2007. Now, nearly 5 years later, most of its content is no longer current. So I will use this spot for publishing my "Frequently Asked Questions" relating to BC-700/900/1000 family of chargers. This list is work in progress and will grow with time. Let me know if you have new questions to be added. Here goes...
[Q1] There are four operation modes on the BC-700 (Charge, Discharge, Test and Refresh). Which mode should I use and when?
[A] Most of the time you just need CHARGE mode. That means put in the batteries and select the charging current desired (500/700mA, etc)
- If you want to know how much capacity your batteries can actually hold, use the CHARGE/TEST function. Be careful not to run this operation if the batteries are freshly charged (doing so may lead to over-charging).
- If you want to find out the remaining charge in a battery, run DISCHARGE/REFRESH and record the 'mAh' number at the end of the first discharge.
- If you suspect your batteries suffer from reduced capacity, run the DISCHARGE/REFRESH operation. Or you can use this mode to refresh your batteries once every 6 months or so. Don't over do it!
[Q2] Why won't the MODE button response when I press it?
[A] Press and hold the MODE button for 3 seconds, then toggle it to change mode.
[Q3] What is the difference between TEST and REFRESH?
[A] TEST starts with a full recharge, then it discharges the cell once to determine its capacity. Next it recharges the cell to full again.
REFRESH starts with a discharge to determine the cell's remaining charge capacity, then it charges the cells back up and drain it down again to determine its new capacity. It wil repeat this Charge/Discharge cycle multiple times until the capacity stops improving. Finally it charges the cell in the end.
[Q4] My BC-700 has been discharging and refreshing for 3 days!! When does it stop?
[A] The REFRESH operation takes at least three Discharge/Recharge cycles to complete. If you use the default 100mA discharging (200mA charging) current for a 2000mAh AA cell, each Discharge/Recharge cycle takes about 30 hours! Terminate the Refresh operation and restart it using 350mA discharging (700mA charging) instead.
[Q5] What is the best charging current for recharging AA or AAA batteries?
[A] For AAA cells the default 200mA is just right. If you're in a hurry, increase the current to 500mA.
For AA cells you should increase the charging current to either 500mA or 700mA. This reduces the charge time and, more importantly, ensure that the charger will not miss charge termination signal and ends up over-charging your cells.
[Q6] How does the BC-700 know when to stop charging?
[A] The primary termination mechanism is "negative delta-voltage detection" (-dV/dt). If this signal is missed, backup mechanism include: high voltage termination, over-temperature shutdown, and safety timer (stops when total charge > 3700mAh)
[Q7] I ran a Charge/Test operation but in the end it shows a capacity reading of "000 mAh". Are my batteries dead?
[A] Most likely the charger missed the -dV/dt termination signal, and subsequently tripped either over-voltage or over-temperature shutdown.
[Q8] I used the BC-700 to recharge my Duracell 2650mAh batteries, and the capacity readings are over 3000mAh. Are those batteries great or my charger is bad?
[A] When you use CHARGE, the 'mAh' reading is for amount of charge going INTO the battery, not what is actually STORED by the batteries. Because the energy conversion is not 100%, you always need to put in more charge, especially if your batteries are old or leaky. To find out the charge stored, use either Charge/Test, or Discharge/Refresh
[Q9] I put in a set of exhausted batteries and one of them shows 'null'. Is the battery dead?
[A] If a battery has been over-discharged, its terminal voltage may fall below 0.5V and the BC-700 cannot detect it. You can kick-start it by using my "Paper Clip trick" (see customer image section for details), or by charging the dead cell in a dumb charger for a few minutes. Then the BC-700 will recognize it.
[Q10] Why can't I tell how much charge is left in my battery instantly?
[A] No battery testers in this world can do that. The only reliable way is to run Discharge/Refresh. However, you can estimate the `fullness' of your battery by looking at its voltage. When you first insert in a battery, its voltage is displayed for 8 seconds. If the voltage is higher than 1.30V, the battery is mostly full and you don't need to recharge it. If it is below 1.20V, it is nearly exhausted.
[Q11] How do I power the BC-700/1000 from my car battery?
[A] You need a CLA (cigarette lighter adapter) with 3V output at a 2.1/5.5mm barrel jack; current rating of 3A for the BC-700, 4A for the BC-1000. For example: AccuPower AP12243 Car Adapter
. An easier solution is to get the La Crosse BC500
which runs off 12V directly.
[Q12] What is the REAL advantage of having an advanced charger like the BC-700?
[A] It allows you to determine the true capacity of all your batteries, and to revive those under-performing cells. Then you can group cells with similar capacities together for best result. Plus it looks cool and is a chick-magnet... just kidding!
[Q13] Is it normal for noise to come out from my BC1000 when it is charging batteries?
[A] Yes. The BC-700/1000 uses pulsed charging current at 25% 1 Hz. So when you set the current to 700mA, internally it is putting out 2800mA for 1/4 second. That's why it emits a faint ticking sound once every second.
[Q14] Why am I not able to see a charge termination even at 500 mA charge rate on my brand new AA Eneloops? (Voltage on the battery was 1.43 V when I manually pulled out. When I insert the same battery again it promptly says full!)
[A] It is normal for eneloop cells to reach at least 1.48V just before the delta-voltage drop is detected. If you remove a cell while it is only 1.43V and re-insert it right back, the charger detects a higher than expected voltage for NiMH cell, so it treats the cell as full and will not recharge it. Otherwise it could miss the delta-V detection from this stage.
[Q15] What is "charge rate" and how does it relate to charge time?
- Charge rate C = charging current (mA) / Capacity (mAh)
- Charge time (hr) = Capacity (mAh) / Current (mA) = 1/C
Therefore 0.2C means a charge time of 5 hours, for example
[Q16] What is the best charge rate?
[A] The general recommendation from battery manufacturers is to keep the charge rate between 0.5C and 1C. Higher charge rate shortens battery lifespan. Lower charge rate may cause charger to miss termination signal. In practice, a rate between 0.25C and 0.5C is preferred if pulse-charging technique is used.
[Q17] If I recharge an 800mAh AAA battery at 200mA, is there a danger of missing charge termination signal at 0.25C?
[A] No. The BC-700/900/1000 uses pulsed current at 25% duty cycle. So when you select '200mA', the actual charging current is 800mA for 0.25 second, followed by 0mA for 0.75 second. Therefore although the DC heating effect is at 0.25C, the charge termination signal is determined at 1C. On the other hand, charging a 2000mAh AA cell at 200mA is borderline too low and should be avoided.
[Q18] I have some old batteries that developed high internal resistance. Will it help by cycling those batteries in REFRESH mode?
[A] The problem with higher internal impedance cannot be reversed. Your best hope is to charge them at the slowest rate, then use them for less demanding appliances such as wireless keyboards. But if they also suffer from rapid self-discharge problem, then you should just recycle them.
[Q19] How do I find out the firmware version of my charger?
[A] When you first connect the charger to AC adapter, the rightmost column shows the firmware number. For example, '35' means firmware v35.
[Q20] How does the AccuPower IQ-328 Battery Charger
compare to the BC-700/1000?
[A] Except for some very minor differences, the IQ-328 is identical to the BC1000, down to the same bugs. But it has thermal dissipation problem and will trip over-temperature when charging 4 cells at 1000mA. See details here: http://www.amazon.com/review/R1W62S0X09QMMQ/
[Q21] Is the BM200 Intelligent Charger
same as the BC1000?
[A] The BM200 has a similar looking LCD panel, and seems to offer many improvements over the BC1000. But it has thermal dissipation problem and will trip over-temperature when charging 4 cells at 1000mA. Read my review on it for details: http://www.amazon.com/review/RRZI4G772IAVR/
[Q22] How does the BT-C2000 Battery Charger Tester Analyzer
compare to BM200 and BC-700/1000?
[A] The BT-C2000 looks identical to BM200, but it has updated hardware and firmware to resolve the thermal problem. The latest firmware v2.1 fixed the REFRESH function and offers better user interface.