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Old 06-10-2010, 05:02 PM
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bluebee bluebee is offline
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Originally Posted by oldskoolbmw View Post
DI water is not recomended as it will not support ion transfer but actually inhibit it.
Are you sure? The Bentleys say to use distilled water (see page 020-23 below).

BTW, how does this improved writeup look:

- Battery: A charged battery is 33.5% (volume/volume%) 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). [Total Volume: unknown but users have reported adding about 20 ml per cell after two years of use]. Replacement Interval: Lifetime fluid (top off only if needed, after removing steel strap, two stickers and then unscrewing the six cell caps, and filling to the fill line which is 1/4 inch or 5mm above the top of the plates at the very bottom of the internal black plastic depth indicator). The OEM battery has built-in hydrometer where green indicates a charged battery and black indicates a discharged battery, and yellow indicates a defective battery. Better to 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 (add or subtract 0.004 to the hydrometer reading for every 10F/6C above or below 27C/80F respectively); and a 12.6 volt open-circuit voltage test across the battery terminals (Bentley 121-5, 121-6). OEM specs are BMW, USA 729905-10, EN 12V 90Ah 720A, SAE 160 RC 720 CCA. Aftermarket batteries are NAPA #7549, Deka 649MF, Interstate MTP-93, Werker model???, Batteries Plus model???, East Penn model??? (need specific model info) with a stamped date code within the last month or two.

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Last edited by bluebee; 06-10-2010 at 05:13 PM.
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