there are plenty of scare stories around about dangers of replacing batteries, that you will need to 're-teach' the ECU if you take battery off, that your electric power steering will go wrong etc. You are far more likely to have problem with battery code and your electric windows may lose their 'auto' setting (but is easy to re-teach, look in your handbook). Leave one or more car doors open during battery change in case central locking locks you out.
best way I have found is to make sure replacement battery same post positions and size as the old one (Japanese cars have smaller diameter posts and they can be opposite position to European cars), make sure it is fully charged and the terminals are clean (use non-metallic scourer pad (green type if you have it). Take the negative (grounded to car body ) terminal off first and replace it last (just in case you touch your spanner down to car body while working on positive terminal (which will make a big spark). Use Vaseline or proper electrical terminal compound to coat the terminals and prevent corrosion (especially positive terminal) do not use normal grease as it is an insulator. Try to fit negative (final connection) firmly in place in one go, do not dab it on and off the terminal as this may cause problems because power to car equipment is jumping up and down.
I have replaced plenty of batteries without any ensuing problems, the ECU may have its 'user' memory reset to base parameters when power is removed, and car may drive differently for a little while, but after a couple of days driving it will build up your profile again.
