I'll stick my oar in, even though its been said
Charging batteries from a source that varies in terms of 'energy output' (both current and voltage) can be difficult. The obvious method would be to only charge your batteries when the energy provided is above a certain threshold - but this can throw away significant amount of energy if its just below this threshold. You will have to, at the very least, separate it into two sections - power conditioning from a generator/alternator, and the battery charging circuit, which can monitor the battery voltage, current, temperature and handle cell balancing.
Lithium Polymer batteries are convenient for intermittent charging, that is to say providing you have an effective charging circuit, you can charge it for a minute, or several hours without the battery having any 'memory'. Laptop batteries do have a memory in a way, but this isn't the battery itself, rather the 'coulomb counter' circuits used to indicate charge level, and battery health.
I would rig your alternator to a treadmill, or a exercise bike, and run some basic tests. A rectifier of sufficient current capacity, and a large smoothing capacitor so you get 'rough DC'. Along with a load such as a light bulb, rated at a higher voltage than you believe the alternator to run at. With two multimeters you can measure voltage and current of the load. This doesn't have to be accurate at all, but it will give you an idea of how much the voltage varies, and what currents it provides under loads depending on how fast you cycle.
Very basic, but that will give you a range of voltages, and respective currents to work with. You can then use this information to design a switching converter to step up/down voltage, or provide a constant current for charging your batteries. Also, the 'constant current' charge of a lithium battery can vary, so the more energy provided the faster it can charge, but also continue to charge at a slower rate when the energy input is low. This will greatly affect charge times, and you may need a circuit to keep track of current and voltage to give you an indication of how much energy has gone into the battery (and how much energy has been drawn from it).
A 7 cell Lithium charger can be complicated enough even with a known stable power source, with a variable one it only gets worse
Your project will be complicated, and probably not that efficient, but breaking it down into parts, and testing each one will help.