2-4 slot charger with USB input (UPD: low current is more relevant than USB)

I am new to the topic of energy storage and in this forum. I have accumulated several AA and 18650 batteries purchased a few years ago for bicycle lights. I don’t use them now, but would like to use an 18650 hand torch and an AAA headlamp. I am looking for a charger that can revive old batteries (if possible). I suppose I need a low current (250mA) and do not need fast charging, 1A will be enough. I consider Liitokala Lii-M4 and Lii-500, but type-C are preferable in terms of convenience.
I am in Israel, many sellers from Amazon and other stores do not send products here. Most items from Aliexpress are available to me. What would you advise to look at in a budget of $ 20 with a current of 250A?
And one more question, can I influence the output current by lowering the input current? If the charger gives 500mA at an input current of 5V/2A, will it give <500mA at an input of 0.85-1A?
Thank you in advance.

Lii-M4 is a newly-released charger and doesn’t appear to have much detailed reviews yet.
It supports 0.5A and 1A charging only. Uses USB type-C power input.
Unfortunately I don’t know if lowering the USB input current will also result in lowering the charging current (maybe not?)

NiMh batteries can usually be revived by doing some charge-discharge cycles (Capacity Test mode can automatically do 1 cycle of charge discharge-charge).
The Lii-500 Engr and Lii-M4 supports Capacity Test.
Lii-500 Engr supports 300mA charge current. (other supported charge currents for Lii-500 are 500mA, 700mA and 1A max).

(The Lii-M4 only supports 500mA and 1A).

Have you checked the Opus BT-C3100? It supports more charge current selection, and has a bit more options and its resistance test is more consistent — resistance measurement is good for checking condition of battery (assuming you check and jot down the resistance of each battery every now & then). The BT-C3100 also has as low as 200mA charge current. Also has a Refresh function for cycling NiMh batteries. In addition to capacity testing.

For modern chargers, you can check the Vapcell S4 Plus (which also has capacity test, and has charge current as low as 250mA. I think these are also available from AliExpress stores.

BUT, how old are the 18650 batteries that you’re trying to revive? If lithium-ion batteries are kept in a severely discharged state, they may not be safe to revive. Or even when revived (from a severely discharged state), the battery will have lost some capacity, or may now self-discharge very quickly due to getting damaged while in the severely discharged state for a very long time.

Xtar VC 2/4.

500mA x 4 slots, 1A x 2 slots for the VC4 and they do li-ions and NiMH.

Just use a solid wall wart that does a true 2.4A.


Opus BT-C3100, Lii-600, Vapcell S4 Plus are very expencive for my needs.
Xtar VC4s seems to fit my budget and it has test and store function. There is one comment on Ali that all 4 slots work in the same mode, charge or test, so you can’t use it for different functions at a time.
When my multimeter will arrive I will measure all the batteries that will be at hand.


Something I didn’t like when I tried the VC4S is that the charging current cannot be user-configured. Assuming that the USB input power can provide enough power (eg. 5v/2Amps), then the VC4S will likely use the highest charging current, depending on how many slots are occupied by batteries, although it can auto-select charging current based on the charger’s resistance measurement of that battery (high-resistance battery will get a low charging current; and low-resistance battery will get a higher charge current, subjected to the limit of the USB power source). The complaint for VC4S is that it may charge AAA batteries that have low resistance (eg. while still new) at a too high charge current (if only 1 battery is charging, since the power will not be distributed to other slots).

Anyway, just mentioning this point… Otherwise, the VC4S has a good number of functions for a USB-powered charger.

So... Xtar VC4/VC4S can only charge two 18650 cells simultaneously. And it has no less than 0.5A current.
VC4L can charge 4 x 21700 simutaneously, compatible with protected 21700. But in rest of the parameters is the same as VC4, minimum 0.5A current too. $15 on Ali.
I see that NiteCore UM4 has 0.3A current (with some manual intervention) in $23-26 budget. Most likely no any capacity analyzer.
At the moment I have three types of cells in use: AA, AAA and 18650. So too high AAA charge current and only two 18650 cells option in VC4S don't fit my needs.

At least regarding the Xtar VC4, it can charge four cells/batteries simultaneously, but only at 500mA.


You’re right, 4x18650 is possible.
I rummaged through the reviews and compared some parameters, and found that few devices have a low current (less than 0.5A) and cost $ 20-25. And only Lii-500 has battery analyzer. So I tend to buy Lii-500.

Clicking on a header will sort by that field:


Remember the CC/CV charging curve. If the cell is only partially depleted, the current will be less than a cell that is fully depleted.

It depends on where you are.


It’s exactly what I did.