Inverter off house LiPO4s to run trickle charger for starter batt?

[Beerlover]

If I have a 100w panel running through a PWM controller to a 100Ah LiFEpo4, which is powers my sailboat's 12v system (including an inverter that I never use), is there a reason I couldn't hook a battery tender to the inverter to float charge the starter battery?

 

[time2roll]

Yes that is fine. Although 100w panel may allow the LFP battery to become depleted. Keep an eye on it and prepare to add more solar.
A direct DC-DC charger might be more efficient.