Keith even though you use your car regularly if the journey is not long enough the battery will not be fully replenished. This is particularly relevant during the winter when extra loads on the electrical system will compromise the battery charge current. A situation can develop where for example the battery is only recharged to 90% of it's remaining capacity then next time on same trip only 90% of 90% and so on in a downwards spiral.

Given the age of battery I would try to reverse this situation by a series (three or four) 24 hour charges using a full smart battery charger of at least 4 amps capability and not a conditioner. This should remove some of the plate sulphation that is presently limiting it's capacity due to above scenario.

Long term and irrespective of cars usage a 24 hour top up charge say once a month should suffice.

FWIW the immobiliser draws very little current and my car with 4.5 year old battery has just started car after a month without use, despite not always practising what I preach blush

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone