The sign for "battery" (as in "I need a new hearing aid battery") is actually the same as the sign for "electricity." Your meaning is made clear by the rest of your sentence.
To sign "electricity," use "X" handshapes. Tap (gently) the knuckles together twice.
ELECTRICITY = "battery"
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BATTERY:The sign for "electricity" can also be used (in context) to mean "battery"
Sample sentence: What kind of battery does your hearing aid use?
= YOUR HEARING-AID BATTERY, YOU NOT-YET CHANGE YOU?
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There is an initialized version of "battery" that uses a "B" hand. This is a "Signed English" version of battery. I see it being used from time to time with Deaf kids that use hearing-aids, but I really don't recommend using this sign. The "ASL way" to sign "battery" is to use the sign for electricity.
If you sign "HEARING-AID ELECTRICITY" it is obvious that you are talking about a "hearing-aid battery." So there usually no real need to ever use the initialized version of "battery" shown below.
BATTERY: (initialized version) (not recommended)
Notes: