I hauled my Spyder to the dealer and left it for a couple of weeks. The tech checked everything, and couldn't replicate the "won't start" problem. Just the same, he checked battery voltage, charging system, both Mode switches, and replaced all the relays in the front fuse box. At the advice of BRP, he also added a ground wire to the coil bracket, oil tank, etc.
He also replaced the failed battery under warrantee, and I have the Odyssey battery as a spare.
Observation 1: the mode button is only to be pressed once, and very quickly. Holding the M button too long (waiting for the message to go away) causes a recycle loop. So, wait for the complete self-test display to complete, let the message scroll for a couple of seconds, then press the M button once, very quickly.
Observation 2: The system checks for transmission in neutral as part of the starting. If the transmission is in gear, as soon as the engine starts it shifts the trans to neutral. I'm now taking care to shift to N before shutting down. Theoretically, if the trans is in gear, holding the brake on allows the start sequence.
Observation 3: The dash-mounted M switch is apparently less reliable than the handlebar-mounted M switch. So, I now use the M switch (on the front of the left handlebar pod) to cancel the scrolling display. It seems to work for me every time now.
Observation 4: Relays are known to fail as a result of low voltage (as when a battery is failing) These are common automotive relays, and I think I'll start carrying a new spare. If the starting anomoly occurs, I'll try swapping the main relay.
Observation 5: Battery connections are critical. It's essential to have clean and tight connections to both positive and negative terminals. A connection that isn't snug will allow voltage and instrument functions, but won't provide the necessary current to power the starter solenoid. I am suspicious that the connections to the Odyssey battery might not have been sufficiently tight. I checked the connections to the currently installed Yuasa, and they are snug (and now greased)
The bottom line is that a good battery combined with proper driver technique is yielding reliable starts now.
I should add that BRP has been very helpful, and the dealer service manager has been extremely cooperative.
pmdave