E39 OEM Battery Maintenance
Prepared by VietSB
NOTE: Perform these steps at your own risk. All P/N's listed are a "best guess", so please double-check with your local dealer. These mods and repairs were performed on my US-spec 1997 540iA (11/96 prod date, M62 engine) but there is no guarantee they will work on other E39's. These instructions are provided for entertainment purposes only!
BACKGROUND: They say it's maintenance-free, but some folks on the bimmer.org board check and top-off their battery cell levels yearly, especially before summer climate arrives. I'll let you decide...
Also, if you drive your E39 only on "select" Sundays, you might want to look into a battery maintainer/charger. Lack of use will eventually drain a battery and with replacements going from $100 (Douglas OEM) to $180 (OEM), proper fluid maintenance and charge level is a very good idea.
- Distilled water (only)
- VDC Electronics, Inc. BatteryMINDer charger/maintainer/conditioner (~$46 including cigarette lighter plug from BatteryMart)
- 3/8" Ratchet, extension, 10mm, 13mm socket
- Proper-sized Phillips-head screwdriver to remove the caps (a penny or nickel might work)
- Squeeze bottle or large liquid dropper
- Good light source
1. Disconnect the negative lead of the battery if you don't trust yourself. I chose to leave it connected since I'm lazy.
2. Remove the 13mm bolt and nut holding the battery brace in place. It's the yellow metal bar in the pic above. If you have a newer E39, the cell towards the front of the car might be obscured by the positive battery lead. Use the 10mm or 13mm socket to carefully remove the lead.
3. Carefully peel back both stickers.
4. Unscrew the cell caps one at a time. Fill with distilled water till the fluid touches the very bottom of the internal black plastic depth indicator coming down from the top of the battery cells. Do not overfill! Use a sports bottle w/ flexible straw or turkey baster to fill the cells with minimal spillage. Unscrewing the cap near the positive terminal might be difficult, but it is possible. They might be fairly tight the first time around, so if you decide you need to use hand tools, please follow my advice about disconnecting at least the negative terminal.
5. Ensure all the cell caps are back on to their original tightness, put the stickers back down, reattach the battery brace, and carefully reconnect the battery leads.
For charge level maintenance, I looked at the following:
- Deltran Battery Tender PLUS!
Sharp-eyed readers will notice the Deltran Battery Tender PLUS! looks *a lot* like the BMW Advanced Battery Charging System, but with the convenience of interchangeable plugs (permanent rings, alligator clips, and optional cigarette lighter). The dealer version might also have interchangeable plugs, but only the cigarette lighter appears to be included. It can be found cheaper at places like Chaparral Motorsports. For occasional use, the Deltran Battery Tender Junior is attractively priced.
Battery Tender PLUS Pros:
- Charges at a higher amperage (1.25A) than the BatteryMINDer (1A)
- Appears to charge the battery up from any voltage
Battery Tender PLUS Cons:
- A possibly biased report of a semi-dangerous failure.
- VDC Electronics, Inc. BatteryMINDer
A nice benefit of BatteryMINDer is the "desulfation" feature. In some cases, it can bring a battery back from the dead, which the sales rep confirmed based on customer testimonials. I'd tend to trust the rep since his company sells both products and they are equally priced. I'm sure that feature isn't always effective, but it's worth a shot. Regardless, both products have fans so they are probably comparable.
- Desulfation capability
- A possibly biased report and feature matrix.
- Small footprint
- Includes a free offer for a battery condition display called SureGuard for $5.95 S&H. It's basically an onboard voltage meter (since our cars lack a visible voltmeter) and also absorbs some power spikes during jump starting.
- More of a "maintainer" than "charger" since it charges slower and will only charge a battery that is above ~10.5V which is sometimes very inconvenient.
Here's a pic of the SureGuard and hard-wired charging connecter in my car for quick and easy hookup. I highly recommend adding a fuse to the positive lead if hard-wiring anything to a non-fused portion of the battery. I hope this doesn't throw off the SureGuard reading or BatteryMINDer charging capability, but I feel safer.
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