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Old 06-10-2010, 09:00 AM
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Do you ever top off your E39 battery (and how much water did you use)?

Do you ever top off your E39 battery (and how much water did you use)?

I'm trying to create a detailed precise one-page summary printout for the dozen fluids in the E39 suitable to keep in your glove compartment or in the Bentleys.

This liquid summary is woefully lacking in the battery section where I don't even know how much fluid is inside the battery, nor how much people generally use to top it off.

Here's what I have so far (please improve so we all benefit):

- Battery: A fully-charged battery is 33.5% v/v sulfuric acid (4.2 Molar H2SO4, ) & pure water, aka distilled, demineralized, or deionized water (Bentley 020-23) with positive plates containing lead dioxide (PbO2) and negative plates of lead (Pb), both mixed with calcium (Ca) to minimize gassing (i.e., loss of water) and other elements (such as tin, antimony, & selenium to harden the plates and simplify manufacturing) in a polypropylene case. In the discharged state, both plates turn to lead sulfate (PbSO4) as the electrolyte loses its dissolved sulfuric acid and becomes primarily water (which can freeze in cold temperatures and the lead sulfate may form insoluble crystals which, over time, reduce the capacity of the battery if it is not recharged immediately after discharge). [Volume: unknown... please help!]. Replacement Interval: Lifetime fluid (top off only if needed). Test at 27C/80F by loading battery with 15 amperes for 1 minute (or just turn headlights on w/o engine running) and then perform a 1.265 specific-gravity hydrometer test of each of the six cells; and a 12.6 volt open-circuit voltage test across the battery terminals (Bentley 121-5, 121-6).

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Last edited by bluebee; 06-10-2010 at 09:06 AM.
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