DS Lite powers on but won't charge - diagnosis?

Recently swapped cases on DS lite. I charged the battery in its old case before swapping them over.
Now they're swapped the battery refuses to charge. There is no light when I plug it in.
However, if I plug it in I can still turn it on and play it (LED is Red).

Much searching suggests it is F1 or F2 fuses. However, given that it can be turned on, does that mean it's not either of the fuses? (ie are they in serial from the power in?)

Any thoughts.