That's similar to the type I use on my v6 when not driving for a while. They are very effective. However it is best if there is easy access to the battery. Apropos the light switch and a need for a t4: would using a replacement temporarily, prior to getting t4ed, pose a problem,; e.g. making the car undriveable or damaging other memory components? If I test the battery for current draw using a multimeter what sort of figures should I find?
Incidently, Seasonal Greetings to every body and thank you for the swift, knowledgeable suggestions/solutions/advice etc.