C58; you're probably correct about battery life. I just sold a five year old 52V, 10 ah battery that was used on a 1000w DD errand bike and a BBS02 off road bike (probably 500 charges at least), but I'm in socal where the ambient temperature probably is >40F - <100F all the time. I never tested the battery quantitatively, but it was very functional (15 miles ride with 3,000' of elevation gain at the five year mark).