Shock horror - Ethel refuses to start

All geared up yesterday for a day's business then Ethel refused to start ! Swore loudly and abused her verbally but it made no difference.
All dash lights come on, kill switch off, whirring from starter motor but no dumpf kerdumpf of pistons going up and down. Never did trust the battery fitted a while back when Orbit Tyres killed the bike at MOT, it does not spin up like the Odyssey battery. So 1st step will be to check that. Got until next Wednesdays Sussex trip to get her started.