If you a looking for long term reliabilty, low cost, low maintenance then do not use Lithium Ion/Polymer. Cellphones/laptops are almost a throw away commodity and the small density, fast charge/discharge characteristics are perfect.
Scaling this up to the energy density of a 33Ah 300+ CCA is cost prohibitive - you do save weight and space by a huge factor, but the charge circuit is more complex. On a slight plus, 4 cells in series give 14.4V so good enough for starting and close to the standard charge rate.
I find it difficult to believe* without some research that they can be directly substituted - Lithium Ion is extremely sensitive to over charge/ over discharge, etc
A new RR could be built to support this, but you could not use the battery as the main capacitor smoothing out the rail, so the electronics become more complex requiring full wave rectification, smoothing and then linear regulation of both voltage and current.
That doesn't mean that you cannot connect it directly to an existing regulator charge circuit and it won't work, but I would not recommend it - way too easy to go outside the safety margins that Li-ion need...
I'm intrigued though so happy to hear any good stories or experience !!!
and for those interested yes look up Lithium Ion battery fires - lots of laptops, phones, ipods, models cars/planes....
mark
* (I've been working on cell phones/mobile devices for the last 9 years)