Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can electric shaver charge batteries installed with reversed polarity?

  1. Jun 7, 2013 #1

    I bought 2-AA (with pins tabs) rechargeable batteries for a Braun electric shaver. Checked the polarity of the old batteries, marked it on the board, and soldered the new batteries accordingly. (In series.)

    First charge lasted 4 weeks. Next 3-4 charges lasted less and less. Now, batteries won't even hold a charge overnight.

    Battery supplier claims that this symptom is classic for reversed polarity...

    Does this make sense? Any thoughts? Could the old batteries have themselves become reversed in polarity? What can be tested at this point?

    Thank you,
    Last edited: Jun 7, 2013
  2. jcsd
  3. Jun 7, 2013 #2
    Well I don't explicitly know, but this is my thought about it =)
    Battery cells store energy in a very interesting way. You have the two sides, the anode and cathode, which are made up of metals and between them lies a, usually, alkali solution. When you connect the end of the battery and complete a circuit. The anode dissolves forming positive ions, since it is a metal, and the electrons give you your current for whatever you have plugged the batteries into. When you recharge you reverse the process by supplying electricity which reforms the anode, but you effectively switch the anode and cathode doing this thus reversing the polarity. And the reason that they recharge less is because some of the ions from the previous anode and cathodes becomes atoms whilst still in the fluid so no longer carry a charge.
    The way i would test this theory is by creating a battery myself, bigger, so I could see what happens... but I think the supplies would be difficult to get because you'd eed an appropriate anode, cathode and electrolyte. What do you think?
  4. Jun 7, 2013 #3
    Check polarity of batteries with voltmeter.
    Is polarity of batteries opposite that marked on batteries?
  5. Jun 7, 2013 #4
    Its hard for me to imagine a consumer product whose batteries are not user replaceable (require soldering) accommodating arbitrary battery polarity.

    How many consumer products where batteries *are* user replaceable work when batteries put in wrong way around?

    My guess is that you got some inferior or wrong chemistry batteries.
  6. Jun 8, 2013 #5
    Thanks for the thoughts. I'm out of town right now, but will check the polarity of the batteries with a volt meter. The "+" and "-" were hand-written in by the manufacturer, and both ends are identically flat, unlike store-bought batteries. So, perhaps they were written incorrectly? Or, if I have reverse-charged them, what will the voltmeter show?

    I wonder if there is some circuitry in the shaver to prevent reverse polarity charging. The shaver seems to run 'hotter' than before while charging. It's amazing to me that there are no circuit diagrams to be found on the internet-- it's as if Braun has done a solid job to keep any technical information to themselves.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook