Split charging has been the tried and tested way to charge a lead acid deep cycle battery for a long time and is still suitable for most older vehicles. Split charging with a relay is not suitable for Lithium, AGM or Gel battery charging as you can not control the correct charging voltage these batteries require. On all modern vehicles we advise to do a test on the vehicles battery to be sure you fit the correct charger as all modern vehicles will now have a smart alternator and will require a battery to battery charger.