Disconnecting the negative terminal might work, but
it might also bring a few other issues with it - it seems that there are a few things that rely on that power being there all the time that could object or make starting just as troublesome.... :dontknow:
Have you considered/tried a small solar panel charger?? If there's regular access to daylight wherever you park your Spyder, then that may well work - it can be made to work admirably for many much bigger batteries &/or higher power demands, sometimes just with an A4 sized panel & light-duty un-regulated charging system...