Have you left charger on for at least 30 minutes with battery connected?
Your system will be probably be different to mine, but let me describe my experience which for the first 25 minutes of the charge was not what I had expected and very disconcerting at the time...
When my Kalkhoff 18Ah battery was delivered it must have been in a very deep state of discharge. There are no lights on the Kalkhoff charger, only the 5 LEDS on the battery. When first put on charge there was a very brief flash of the first LED every few minutes. I went to get a mains power meter to measure the mains power going into the charger. I saw 60 watts going in so I kept on watching and checking whether anything was getting hot. It wasn't.
After about 25 minutes the first LED started flashing at about once per second which is normal during charge up, and from this point to full charge the LED indications were normal i.e. what I have seen every time since then when charging.
That first charge took over 12 hours about 1.5 hours longer than the battery now takes to fully charge from a discharge to the point of low voltage cutoff.
My battery had a manufacture date code in Jan 2011, I received it in April, and has been working very well. It must have been in a very deep state of discharge when I received it.