Lithium battery installation

Hi

We have bought a new Lithium iron phosphate battery for our caravan along with a solar suitcase for when we are off grid. We have bought a specific charger for this when we are at home.

We are not sure if we can charge the battery from the old system (previous lead acid battery) or if we need to change the on board battery charger running from the alternator. Anyone got any experience of this? The chap who serviced our van last week wasn't sure. 

Thanks for any advice.