I use Odyssey in all my bikes.
Battery not the place to go cheap IMO.
Shop the internet for best deal.
I did this mod to my 04 GS for jump starts.
Did not use any "adapters", just flattened/reshaped the esisting terminal ends.
Have never had to jump start the bike but have used my bike to jump others.
Might try cleaning the starter as well.
Hall of Wisdom is your friend.
3 Continents - 7 Countries - 50 States
04 BMW 1150GS Adventure
02 BMW K1200LTe
05 Yamaha TW200
BMW MOA 109760
AMA Charter Life Member 518333
International Fellowship of Motorcycling Rotarians