By male battery I mean the threaded part protrudes and is threaded around the outside. Female batteries have a recess that is threaded on the inner wall
If the battery is at least 9mm diameter...
If battery is MALE
may be KR808D-1 / 901, or KR808D-2
If the battery is FEMALE
may be RN4081
may be 510 threading (306, L88b, 510)
or highly unlikely 801
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If the battery is under 9mm diameter MALE (skinnier than a 510)
May be M401
(else out of luck - since I never saw an adapter for E8)
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And if none of those work, you are out of luck
And NOTE!!!! If you figure out which threading it is, that does not mean your batteries are compatible with that model's charger or vice versa. Some models have reverse polarity batteries/chargers and will fry some other models with the same threading.