It doesn't have a plug for direct 220V supply, but a cable with a USB port and a Type C end, so it only works with a phone charger, for which you have to make sure the amps are at least 2, otherwise the batteries won't charge.
If you put them in pairs, they must be side by side, e.g. positions 1-2 and not 1-4. If the red light comes on with pauses, it means it is discharged and the charger is "checking" to see whether it can charge it. If it does not stop after a few minutes, this means the battery is fully discharged or damaged and should be recycled. It turns green when it is fully charged. A little care with the "pressing" because the spring clips do not hold it 100% correctly and there is a chance it may fool you because it is not fully pressed in, making it seem like it is not charging.
Would I buy it again? No, because yes, it is a "smart" charger, but it does not take power directly from a wall socket and it does not have a good contact point on the + side for the battery to grip firmly, so it slips easily and you end up waiting for it to charge for nothing.