Got the Shorai 21 model in my 2010 GSA with ESA (actually Ohlins ESA). Had major problems with the 14 or 16 model, stay away from that. Initially it was recommended as the correct model, but it isn't powerful enough. No size sizing with the 21, but she starts well. Stock was 2.5 years old, sometimes slow to crank. Haven't gone through a winter yet, but warming is recommending before starting, but a bit difficult when your headlight doesn't come on until the bike starts.