Originally Posted by _cy_
follow link in my signature if you need details why ...
have posted this several times, but here goes again:
for most folks, my advice is go with AGM. unless weight is totally critical. AGM has one of the main advantages of LiFePO4 which is very low self discharge. unless one has a large parasitic current drain. trickle charger will not be needed for LiFePO4 or AGM over the winter.
some bikes normally have a small self discharge. for those bikes a trickle charger will be needed regardless of what type battery is used. Your lead/acid battery charger may or may not properly charge LiFePO4 batteries.
if you've got a modern adventure bike and decide that it's worth $$$ to save 10 lb or so over AGM or Gel. forget the marketing hype mfg use to calculate which battery to use.
use actual amp hour rating less 25%. note this is for modern Adventure bikes, which has one of the highest battery demands of any bike. example, if factory ratings is 12 amp hour x .75 = 9 amp hour actual LiFePO4 amp hour rating.
some bikes that only are used in fair weather can get by with much lower LiFePO4 amp hour ratings. one advantage of LiFePO4 batteries is ability to deliver larger amps for size, while maintaining a very flat discharge cycle.
learning how to start your bike with LiFePO4 in cold weather is mandatory. yes procedures are different.
take mfg amp hour ratings with a bucket of salt... use real amp hour ratings to size your LiFePO4 needs. LiFePO4 batteries when sized properly are robust, super lightweight batteries.
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.