RG
In your situation, there is no such thing as overkill. If, God forbid, you have another severe alergic reaction your life may depend on your ability to get off the island immediately.
If it were me or a family member in that situation, I would much rather simply change a battery switch position than need to get into the engine compartment and mess with jump starting the engine. It isn't really all that hard to remember to change which battery you are using every week or two in order to keep both batterys fully charged!
Silver Duck