If you're not using the other bike this winter, why don't you swap the heated grips onto the Monster? I think they are fairly universal, but then I've never fitted any.
Had you considered heated gloves and heated socks?
A friend of mine has occasion to walk fields this time of year and swears by his heated socks. He reckons a charge lasts all day and only ever needs to use the low setting.
Expensive, but are they though, If they keep you comfortable?
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