Here is the battery of quality proposed by FULBAT. This YB9L-B of 12V and 9Ah has a length of 137mm, a width of 76mm and a height of 140mm.
Mounts on several models but is standard on motorcycle HONDA 400 VFR R NC21 1986 and 1987
Very simple, made level with acid that comes with the battery. Then load the 24h with the plugs open! Let it rest 1h, close the caps and mount it on the machine. Once mounted and connectors put, grease the terminals and protect the positive. Being serviced every 12 months, make the liquid level with deionized water or even acid and recharge the 12 hours.