Mk6 golf battery low

[Pinewood]

Sons golf has been standing idle over the Xmas period. Tried starting it today and nothing. Still able to operate the central locking doors.
Should I
1. buy a cheap old school charger
2. Use the jump leads across my X3 to his
3. Buy a fancy (expensive)  ctek intelligent charger

Until now, his battery has been fine as it only stands still a day or 3 at most.

Your opinions would be helpful.
If I do use my car to jump start his, where would the points be? (across battery in rear, or points under bonnet)

[snrbrtsn]

I’m one of those buy cheap buy twice types,
I’d buy a ctek intelligent charger, though selfishly making sure you choose buy a model with high enough amperage to cover the x3 as well
The benefits of the correct charger being it shall notify you if a new battery is required

Re jump starting, use the under bonnet connections

My ctek mxs7.0 has paid itself time and time again, primarily on X5 garden ornament though recently on neighbours garden ornament, the benefit of the model is the reconditioning cycle that takes a day or two! Though does restore things moreso as we both know the cause is ultimately lack of use

[Pinewood]

Thanks for that. I will go ahead and buy a ctek intelligent charger. We got the car going and he is out on a 20 minute run, which is difficult for him, as I asked him to stay local and turn OFF the stereo