Is there a minimum battery charge rate?

I have a 5kW GivEnergy inverter with a 5kWh GivEnergy battery, set at present for charging from solar only. Today has been a very cloudy, wet day so the solar input has only been around 350-400W for much of the day. The basic house load has been around 300W, leaving only 50-100W spare. I would have expected that to charge the battery, but instead nearly all the time that 'spare' has been exported. There are settings for a maximum charge rate, but I see none for a minimum rate. Is there a pre-set minimum charge rate.

Our Inverter and battery are set up for solar only too presently. On dull days (like today) and the house is taking most of the generation the batteries are charging at times with just a small trickle of charge, just now it was 41W and I have seen it much lower than that. As far as I know, there is no minimum value.