Electrical problem
1987 Audi 5000 Front Wheel Drive Automatic 180000 miles

I ride bicycle to work and don’t drive much – even in winter (live in Missouri). I recently changed a battery that went bad. How can I increase the life of the battery? Will just disconnecting the cables and leaving the battery in the car be sufficient? Or should I take the battery out of the car and keep it inside the house?
Any particular solar trickle chargers you would recommend?
Thank you for your help,