Mine is mentioned here: [MyL5] Australia/New Zealand - #58 by irvinewade
I think they tell me that this will overcharge the battery if done to completion but that doesn’t matter for your purposes. Charge for only 4 hours. That might be about half done if the battery is completely flat to start with. A half-charged battery will be fine to demonstrate whether your problem is non-charging of the battery or is something else.
Do you have a multimeter so that you could verify that the battery is basically flat to start with and verify that the battery is somewhat charged after 4 hours?