I'm afraid that if it wont hold a charge then its knackered , the best advice for looking after a battery is to use something like the Optimate 3 and leave it connected , i have 2 of these one on my Virago and the other a MST battery gaurd on my Hoodie , more info below ,
OPTIMATE 3 SP - Automatic battery optimisation
Designed for 12 volt starter batteries from 2.5 to 28 Amp-hours capacity.
This is the perfect tool for regular or long-term maintenance of batteries not in daily use.
Suitable for all types of rechargeable lead-acid batteries: filler cap types; absorbed acid "MF" for motorcycles; valve regulated (VRLA); & GEL-electrolyte types.
Supplied with two interchangeable connection sets, one with clamps for bench charging, the other with in-line protection fuse and eyelet terminals for permanent connection to the vehicle’s battery.
Since i have used them i havent had to replace a battery .
Mike