When it comes to charging batteries its best to know exactly what up with the charger and the batteries you are using.
I did it so its fine for you just doesn't cut it. You would feel real bad if he burned his house down or got battery acid burns from your knot knowing.
There have been several instances her on this forum where battery charging has caused major issues. Its always best to be absolutely sure that you have the proper combination. Even then, you need to keep an eye on them until the combination has proved itself.
-Ed