Battery replacement seldom causes issues, but you do need to be careful. Always disconnect the negative (-) black connection first, and refit it last – and always take care that no metal object bridges the two electrical contacts at any point.
You also need to be aware that disconnecting the battery can affect the car stereo – so make a note of any codes that need to be entered in case the power is cut.
In some cases it may also affect the operation of 'one touch' mode on some electric windows – and they'll need to be 'taught' again.
Swapping over a new battery isn't too taxing and you seldom need anything more than a basic socket set and a wrench.
You may have to remove a battery cover, which is usually clipped on, and you may have to fish about down the side of the battery to find the clamp that holds it in place.
The only issue you could encounter is that the nut that screws onto the clamp may require a deep socket, otherwise the threaded portion of the clamp could foul on a regular socket.
Batteries have a shelf life so over time will need replacing. But if you can keep them correctly maintained they can last a lot longer.
Batteries hate being discharged, so you never want to let them run too low.
Avoid operating electrical items for too long while the engine's off, and if you intend to leave the car unused for any length of time it will be worth using some kind of trickle charger to keep them topped up.
If you do suffer from a flat battery, make sure the rest of the charging system is working correctly before refitting a new one, otherwise you could find yourself needing another battery in no time at all.
A battery, if correctly looked after, should last for around 5 years, and it's not unusual for them to last a lot longer. The better you take care of it, the longer it will last.
The actual act of replacing a battery will cost you nothing as long as you already have basic tools.
The main outlay will be for the battery itself, which can cost as little as $50, and as much as $200 depending on your application.
Always fit the same, or larger capacity battery to your car, and never smaller.