I have had it since April 2020 and it works frequently. Every four to five days, I charge 18650 batteries sometimes, and every six days, whether it's fast charging, slow charging, or faster, depending on the adapter you have, that is, the current the adapter provides. The UMS4 charger has had a few glitches like not reading the battery correctly and some silly errors that occasionally appear, but despite that, it doesn't hesitate, you just take out and put back the batteries or the battery that it didn't read, and it starts charging. Don't be scared of these errors, they happen very rarely and it may take some time for it to happen again, just make sure to monitor the batteries for a few seconds when you put them in for charging, in case it gets stuck and doesn't read a battery, and after hours, you realize that the batteries or the battery didn't charge. Anyway, whenever you use battery power, you have to be present because you never know. For example, after a few years of use, last December 22nd, one of the two coffee 18650 LG batteries reached such a high temperature in the charger that it almost exploded (possibly) because the battery was burning excessively, and I wonder how it didn't burst. Luckily, I checked the charger. I took both batteries out and took them to recycling and immediately bought a new pair, and everything is fine. They lasted for 4 years of use, so they held up well. The charger also has a fast mode, but you have to activate it by entering the menu, and it is mentioned in the user manual how to do it. In conclusion, since April 2020, it works on average every five days or every four days, and recently every two to three days because I use an electronic cigarette with a 0.14-ohm resistance, and the batteries easily drain, so I have to charge them more frequently these days. I also charge batteries for a Nitecore flashlight. Buy it without fear. And kids, BE CAREFUL when charging batteries of any chemistry and charging speed, the charger should be near us, we must monitor it for any dangerous increase in battery temperature (especially in summer), but frequent monitoring during charging is still necessary. Also, when you are away from home, do not leave any charger to charge any batteries because you never know. It's better to disconnect the charger from the power, remove the batteries from the charger, and when you return home, put the batteries back into the power for charging and continue. In January 2024, the mini USB connector detached from the charger's circuit board. It is the female connector behind the charger, and initially, I had to adjust it to fit properly so that it could charge. On January 18th, 2024, I unscrewed it to see if I could fix the connector with solder, but it didn't work. I got frustrated, and I will buy another one with a type C connector this time, and it will still be Nitecore. If it breaks again in the future, I will buy a charger from another brand.

The build quality is very good and not like some cheap Chinese chargers. It charges various types of batteries without needing separate chargers. The USB it has is very useful so you can have it on a power bank, solar panel, etc. I use it to charge only lithium batteries (Li-on). The screen it has is very good because all the information is displayed clearly, and the screen is LCD. It also has fast charging capability (QC2.0) which can fully charge a 3,000mAh battery in about an hour (I have tested it), but you need to have a fast charger for this function to be available. You can also choose the current voltage or how fast you want to charge the specific battery. There is also a battery restoration function that can restore lithium batteries (The screen will display "EE" if the specific battery is damaged or if it is inserted upside down). The only problem I had was when using AAA batteries, the information is a bit unreliable compared to lithium batteries. However, it is worth the money because it has a 1-year warranty, but you need to have the receipt with you unless it was purchased online. I would definitely buy it again.

First impressions. Good build quality, with quality plastics, readable and bright screen. The contacts in the slots are soft, while according to the company it is made 100% from slow-burning materials, thus presenting resistance in case of ignition. It essentially charges all types of batteries, so it will definitely cover you. In terms of practicality, 21700 batteries fit only in slots 1 & 4, for fast charging you will need a quick charge charger, otherwise you will receive speeds similar to the D4. The more batteries you charge simultaneously, the slower your speeds will be. The screen does not turn off in standby mode, which is a big mistake in my opinion, in the older D4 the screen turned off. Overall, a good charger, of good quality, which in my opinion is sold at a higher price than it should. You can do the same job with about half the money. However, if you want something of quality that will last for years, then give the extra amount.

UPDATE. In less than two years it broke and the representative informed that it has only one year warranty. In the end, it is a bad product with poor support.