I've seen that BSFC chart as well (have it in my Google Drive Insight folder, even) and I couldn't tell you which one is right, but the one I posted follows the more typical pattern for small engines.
Bear in mind that anything below 230-240 is more efficient than most other (non-diesel) engines you can buy.
The basic design of a grid charger is that you want an isolated fixed current power source of 300mw or less that can provide at least the maximum voltage that the battery will have (which is around 175v), a 12v source to run the cooling fan, and a diode to prevent current from flowing backward. Two cheap 90v eBay LED drivers in series works great for this, or three 60v.
http://ecomodder.com/forum/showthrea...d-29288-8.html
I believe this would work:
2 Pcs AC85 265V 30 90V 300mA Power Supply Driver Adapter for 18 25X1W LED Light | eBay
"Meanwell" is also a fairly trusted brand, if you'd prefer.