Xf new owner major issues !!!!!!!

[Amw]

After driving a 2.0 diesel x type for years with no major issues a 2.7 diesel 2008 xf came to me with a blown engine decided to take it on as a project had engine replaced with one from a 2.7 s type diesel after fitting it be came appartant it had a dpf issue that is what probally blow original engine replaced that with the one of the s type straight swop and everything was good while in garage a few faults where showing intermittently gearbox,dsc,handbrake I think that was it mechanic said he thought the battery was bad because he kept having to use booster pack so when i got it back i bought a brand new battery removed old one fitted new battery dash went clear of all faults car started and drove as it should took It for mot taxed it and was more than happy had a coupe of short journeys a coulpe more very short journeys 1st day parked it up.  (I now know you are better locking car all the time which we did not over the coulpe of short journeys) went to it on the evening of the 2nd day and the dash started flashing with all kinds of faults, recharged battery hoping it was my fault for draining the battery by not locking the car charged the battery but faults still showing car would start and drive this morning but have not drove it as still showing faults.

Put small pulse charger on battery this morning opened it a couple of times started it a couple of times noticed charger regeristing full reading 5 bars after opening and starting car then reconnecting charger battery which was now reading 1 bar charged it to full again removed boot Bulb just in case that is staying on, unclipped charger and also disconnected both terminals on actual battery see if that would clear faults again opened car started it still showing loads of faults turned it off reconnected charger showing battery well below half again recharged again did nothing different opened car started it and dash light up as it should no faults what so ever car started as it should turned it off checked battery again very low recharging at the moment as if battery gets slightly lower a think all the faults will be back on the dash !!!!!!!!

One thing i have noticed is the keyles entry does not work as it should I can open the boot with fob in pocket but not in house drivers door I can open with fob in pocket or in house (not good as parked on street so anyone can open door) but it triggers alarm till I click open on fob 3 other doors do not open till i click fob could this fault be something to do with battery drain on start surely it is not right to near flatten a brand new battery !!!!! I have everything audio,fans,lights etc turned off.

Sorry for length of 1st post just needed to tell the full tale

Any help with these issues from members would be very much appreciated thanks in advance.