Hi
I have try the charger function there days and it work well , without a charger IC and just use a diode , we also can changer the battery nearly full about 4.1V , and can use more than 2.5 hours …
so i suppose maybe your battery is bad , and maybe you charger it to long (10 hours) , the battery has a protective circuit but the DSO has not a charger circuit , so it maybe broken the battery if you charge it too long.
if you can’t found a battery to replace it , that we can sent you a new battery …sorry for our neglect that have not to remind you about the charger Attentions , it will be add to the manual next time.