there are two common solutions for the batterie problem.
1: as cheap as possible. Maybe you will need to replace this one every year
2: high tech beats it all. Hawker? LiPoFe?
I had a lot of cheap ones. As idid not use my Nordie very often (shame on me) i always had troubble to start. So i bought a rather expensive Varta. Crap...
Now i have a sealed Intact.
Since two years no troubble. The Nordie is always starting without problems.
No need to charge before riding. Just plug in and forget.
I hope this will last for some more years
Of course it was not that cheap. But not much more then the 'wet' Varta type.
If you are not in a hurry you may check out the offers on xbay.
ciao joachim