Marren2016 the battery CELLS should ideally be between 20 and 40 degrees. Below 20 degrees, and depending on what BMS firmware you are on, the battery starts reducing its discharge and charge rates. The actual slowdown depends on BMS version, but it starts at 20 degrees C and reduces further at 10 degrees.
Note this is the battery cell temperature, not the battery motherboard temperature. You can’t get this information from the givenergy portal or app, you need either RubikCube’s Android app or GivTCP.
But if your battery is outside or in a cold location this could well be the cause of the reduced throughput.