From a previous threas:
The battery for the 175/200/350 and BS-7 electric start is a 12N5.5-4B. It measures 5 5/16 X 2 13/32 X 5
3/16 with the positive lug opposite the drain line.
Richard Clark had stock of the original batteries. Give him a call at 812-944-1643 8am -6pm EST Only Weekdays or e-mail
at bsparts@aye.net.
If you try to buy it from a dealer or battery supplier, you'll find it isn't available. Use a 12N5.5-3B instead. It is the same size, but has
the drain tube on the wrong end, which really won't hurt anything. Be careful and do not get a 12N5.5A-3B, it's not the same.