As long as the voltages are close it won't cause a problem. A 48V sla pack and a 13s lipo pack will work well together, but that's about the only combo that will.
someone should explain to you that the peukert effect on the lead acid battery will cause the voltage to drop on the lead acid battery and draw charge from the lipo to restore it.
it is common knowledge that you can only combine batteries of different chemistries and potentials with lead acid through diodes on the output of the lead acid battery.