Cat GPS systems and trackers should be as lightweight as possible.
Cats are not as heavy as dogs, but a tracker which is too heavy could also make them uncomfortable or unable to navigate properly, including when needing to stay balanced if jumping or walking along fences etc.
Look for something under 40g, but the lowest you can go, the better. Be aware that some of the heaviest models may only be suitable for cats over a certain weight limit.
Obviously, trackers have to be powered by a battery. But this can either be rechargeable or replaceable.
Which you prefer will be a personal preference. Rechargeable ones will need to be charged every day or two, and while there is no guarantee how long replaceable ones will last, it can be around one year.
Think about your cat – if they are free to go out at night, or go out for long hours, a rechargeable one may be impractical.
For many GPS trackers, this is pretty unlimited and certainly will cover however far your cat goes. They use local signals to alert your phone and keep it updated.
But trackers which use other forms of signal, such as Bluetooth, will likely have a limit, so you will have to think about how far your cat goes and whether this is practical.