Originally Posted by def
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.
huh ... one of the advantages of Lithium batteries is it's ability to deliver HUGE amps.
but drawback is extra costs as compared in equal amp hour energy delivered. more amp hour capacity = more $$$
this is why LiFePO4 batteries found it's first non-electric vehicle acceptance in the marketplace in Motorcycles and not in applications like starting diesels or cars. to create a battery with enough amp hours to support those applications. costs would exceed benefit.
what's it worth to you to save say 10lbs.... for the weight wienie paying $$$ for carbon parts for his race bike and/or wanna be race bike. those are some of the cheapest lbs one can unload.
but for most folks ... best replacement battery still remains AGM. unless of course it's worth all the $$$ to save those 5-10 lbs.
yes ... one can successfully use LiFePO4 batteries in the most demanding applications. but the amp hour capacity has to be there. my recommendation is actual lead acid amp hour ... less 25%.
if you follow most lithium battery mfg suggestions. you'll end up with a battery that supports your bike in the summer. NOT for the winter.
R1200GS has some pretty demanding requirements. including needing reserve amp hour capacity to crank bike over repeatedly if your bike should go down from contaminated fuels, etc. there will be times pounding on fuel pump while cranking and cranking will get your bike back up again.
for cold weather, one needs to understand warm up cycles consumes amp hours. starting procedures has to be learned to start your motorcycle in cold conditions.
your heated gear doesn't understand all those fancy PB/EQ ratings battery mfg use. heated gear draws real amps... if your lithium battery say has only 4.6 amp hours. then your heated suit uses a chunk of that reserve just before you put bike away.... guess what happens next morning?
above is why for most folks ... my recommendation is to stick with AGM. but some of us are willing to pay the toll to save 10lbs. not likely someone trying to sell you a lithium battery will inform you... probably because they don't know better.
here's a chart listing voltages with corresponding battery charge state