Question-What year is the sled and how old is your battery and have you had it checked as to taking a full charge, or is it partially dead/old? The trickle charger, is it giving the battery a full charge, or just keeping it somewhat "Alive" for the next use, if it's in a cold area of storage?have you thought maybe of using a battery "Tender" instead?The Battery Tender is a 1.25 amp battery charger that automatically switches from full charge to a float charging mode and then monitors the battery.
When the battery is accepting only 0.5 amps, the Battery Tender switches into a float charging mode. At this point both the current and voltage of the Battery Tender decrease. The current drops to 10 ma. (virtually no current) and the voltage is 13.2. The gassing point of a battery is 13.8 volts; therefore applying any voltage greater than 13.8 for an extended period of time will damage the battery.
Trickle chargers decrease current but will increase voltage to upward of 20 volts and continue the excessive gassing action that is most detrimental to the life of batteries. Try searching for this unit, "C Tek Multi-use 3300" battery charger, it says charger, but I use it and many others do. It's the best thing going and works on vehicles as well. It comes with all you need to quick connect to the sled's battery when you park it.
What kind of fuel are you using? Higher octane can make it a pig to start any machine with.I know with the turbos, if we use say C12 (107 octane) in there at -20, it is really hard to start, where the 91 and less is much better.
As far as oil, if it's broke in etc, have you tied say 0-40 Amsoil synthetic 4 Stroke, or 0-30 Mobil1? It helps in cold starts as well.
Just trying to help, as my wife I had an '07 Phazer as well before.