Absolutely imperative. Charging LifePO4 batteries directly off the main circuit absolutely destroys them--and then they fail suddenly, completely, and possibly catastrophically--you will have zero power. (contrast to how a lead acid fails--it gets weaker over time--you usually have /some/ power even when it needs to be replaced)
LifePO4 is safer--it won't ever catch fire, but it will lose ability to hold a charge and become a doorstop. It might get hot, not sure on that, but they are definitely much safer than Li-ion.