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Old 11-20-2012, 09:56 AM   #14
Chopper Rider
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Joined: Jan 2005
Location: On a set of 50,000 mile tires.
Oddometer: 15,167
Originally Posted by def View Post
The BMW boxer engine requires quite a bit of starter motor torque to spin the engine past compression stroke, especially at cold start. As each piston approaches TDC during starting, the starter motor current demand increases rapidly placing increased demand on the battery and other starter circuit components.

Li FePo batteries do not respond to this rising rate demand as well as a lead-acid battery. Hence, these batteries don't perform well in engine start applications. As such, if a Li battery is used in this application, considerably more battery capacity should be chosen over lead-acid to insure reliable starting.

Also, my diesel motorhome powerplant has a compression ratio of about 15.5:1. When cold, the starter needs lots of CCAs to spin the engine successfully without overloading the starter circuit. If the batteries are not fully charged, the current diminishes as pistons come to TDC placing further demand on the starter circuit, starter solenoid and wiring.

Yes, LiFePo batteries are light weight. They are fine for applications where there is a kick starter and the battery is used for ignition such as on moto cross bikes.

As I stated, they aren't ready for prime time just yet IMO.

I know you're an expert and all, but have you tried a Ballistic battery on your boxer?
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