It really does sound like an experience I've had here in the U.S. with a similar device. I had an "off brand" 18V cordless drill/driver such as the one depicted and it came with two batteries and the charger. After a few months the drill would work very well for a predictable amount of time, say, an average of 10 days with normal useage. The drill would lose power and it was time to change the battery. The other battery would only last 2 or 3 days under the same conditions. Ours, here, have no battery condition indicator. However, when the battery is mounted in the charger, it has a light that changes from red to amber to green as it achieves charge. Both batteries would charge to that indicated level in about the same time but one just would not "hold" the charge. I wound up buying another and it works very well. Obvioulsy there was an internal problem in the one battery...
Best of luck!