NITECORE Digicharger D4 LCD Display Universal Smart Charger

Ok, let me have my say about this battery charger. Pretty much all reviews are more than positive and yes - it is a good charger (with some concerns). But is it really "the most advanced" charger as it states in its own manual?

Let me start with the overwhelming advantages:

• It charges almost any usual battery on the market (I will exclude NiZn batteries since they are rather unusual anyway), just to mention them: Li-ion / IMR / LiFePO4: 26650, 22650, 18650, 17670, 18490, 17500, 18350, 16340 (RCR123), 14500, 10440, Ni-MH / Ni-Cd: AA, AAA, AAAA, C.
• Independent slots - monitors and charges independently (but only 2 charging circuits, see further below)
• Battery type is automatically detected + different charge modes (Constant Current (CC), Constant Voltage (CV), -dV/dt).
• Low current charging mode for small capacity batteries (that is what convinced me to buy it)
• Attempts to charge fully discharged batteries.
• Hard time limit to charge - max 20 hours per battery - then it supposed to stop.
• Option to use 12V adapter.

At that point, it is pretty convincing that we are talking about rather decent battery charger. But here is what I think it is missing (or I am missing compared to some older chargers I have mentioned before IPC-1 and CM-410).

• Does not show how much it was charged. For CC mode it is proportional to the time the battery was charged, providing that it did not change (i.e. you have not added third battery in the middle of the process)... 
• The charging current drops from 750 mA to 375 mA if you charge more than 2 batteries at the same time... The reason: "The charger has two charge circuits, one is serving slot #1 and #4, the other is serving slot #2 and #3 using time sharing" source. 
• By the way, I measured 44°C/111°F during charging, which does not comfort me much...
  There are reports for 60°C link (Russian language). Also here.
• There are no discharge, test or cycle modes as seen on other advanced chargers.
• Will not restart charging if battery voltage drops (voltmeter readout freezes when charging is finished) source.

Now, to be honest, the disadvantages are clearly not a dial breaker. I will certainly try to use the NITECORE as my main battery charger (it is inevitable with the Li-ion batteries) and I need to use the CM-410 for the special cases where I need to deal with old batteries that either need a "cycle" to refresh or to establish that they are gone.
Update 2016.03.27: I will certainly not use it to charge NiMH batteries. It appears that -dV/dt mode cuts too late the charging current, which leads to significant heating of the batteries and the device. I can only share somebody's else opinion on the net that "...this is not a charger to leave unattended..."

It is worth also mentioning, that you want to be sure that you got authentic NITECORE product. Here is how to do it:

COUNTERFEIT ALERT TO NITECORE CHARGER BUYERS
Just to mention:
I was not able to check my validation code. I was not able to enter the correct security code" for more than 10 times. Scanning the code was the same story...

IDENTIFICATION GUIDE FOR NITECORE CHARGER USERS

I got a bit worried with the text explaining the following "Physics behind: The battery positive pole contact points and railings in the slots of a legitimate Nitecore charger are made from pure copper, a non-magnetic material with high electrical conductivity."

I agree with most, but pure copper is rather soft and does not have silver color.... and you know, most wires are done from copper... Needless to say that the magnet sticks to my rails...


Update 2016.03.20: Somehow, today, I measured temperature of 50°C while charging. And this is how I am continuing now...

... now I know, what will be my next small project - adding "intelligent" cooling rig. Seems backward, but 50°C is not the way I want to treat my batteries...

Inevitably, I wanted to know "what is resonable temperature during charging?". Here is what one can find (the most interesting is highlighted in blue):

3.8.4 NIMH Temperature and Charge Efficiency

The recommended charging temperature is between 10°C (50°F) and 40°C (104°F). If a NiMH battery is exposed to high temperatures (above 40°C, 104°F) due to overcharging or external heat sources, the charge efficiency (increase in stored cell capacity per unit of charge input) will be decreased. In order to avoid decreased charge efficiency, batteries should have charge control methods applied to limit the amount of overcharge heat that is generated. In addition, it is critical to not place batteries in close proximity to other sources of heat or in compartments with limited cooling or ventilation.(source)

Charging Nickel-Metal Hydride

Chargers for NiMH batteries are similar to NiCd systems but require more complex electronics. To begin with, the NiMH produces a very small voltage drop at full charge and the Negative Delta V (NDV) is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and degenerating cell match diminish the already minute voltage delta further.

A NiMH charger must respond to a voltage drop of 8 to 16mV. Making the charger too sensitive may terminate the fast charge halfway through the charge because voltage fluctuations and noise induced by the battery and charger can fool the NDV detection circuit. Most of today's NiMH fast chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.

NiMH batteries that are allowed a brief overcharge deliver higher capacities than those charged by less aggressive methods. The gain is approximately 6 percent on a good battery. The negative is shorter cycle life. Rather than 350 to 400 service cycles, this pack may be exhausted after 300.

NiMH batteries should be rapid rather than slow charged. Because NiMH does not absorb overcharge well, the trickle charge must be lower than that of NiCd and is set to around 0.05C. This explains why the original NiCd charger cannot be used to charge NiMH batteries.

It is difficult, if not impossible, to slow-charge a NiMH battery. At a C?rate of 0.1C and 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100 percent charge. Overcharge could occur even though the NiMH battery feels cool to the touch.

Lower-priced chargers may not apply a fully saturated charge. The full-charge detection may occur immediately after a given voltage peak is reached or a temperature threshold is detected. These chargers are commonly promoted on the merit of short charge time and moderate price. Some ultra-fast chargers also fail to deliver full charge.(source)