Dave,
With the battery at 13.07V (not at float voltage yet), it dropped to 10.85 and rebounded to 11.01 during crank, and this time it lit quickly. On shutdown the battery voltage was 13.05V, no significant drop in power which is not surprising given about three to four seconds of draw. It appears XS is going to want me to send my battery to them for a complete diagnostic check, to know for sure if the battery is weak, or if it simply does not have sufficient power for my needs. I'm to talk to a specific guy tomorrow and find the path forward.