Only the BatteryPlus35 and BatteryPlus35-II-HA are compatible with lithium LiFePO4 batteries. If your BatteryPlus35 is not an HA or II-HA, then it is not compatible with lithium LiFePO4 batteries.
Lithium LiFePO4 batteries may be sold/marketed as a simple drop-in for a lead-acid replacement, but they all require a charger with lithium profile.
Drop-in replacement lithium batteries may not have a standard lithium discharge curve, so state of charge indications may not continue to be accurate.