B1500 strange starting issue

[London]

B1500 went dead on me and would not start - no lights on dash nothing having been running fine. As an emergency fix I put the battery in it from my electric fence which was a physically larger more powerful battery and started up.
the odd thing it having replaced the original battery with a new one it still will not start - it only starts with the larger electric fence battery.
have checked dynamo - works so seems to be an ignition problem But not sure what? Any idea why a bigger battery would work but a ‘smaller’ one wil not? Both 12v and both putting out 12.6-12.8V
thanks

 

[Russell King]

Larger battery may be able to spin the engine faster?

What does it do with the smaller battery? Spin and never starts or just won’t spin the engine at all?

Clean both of the battery cables at both ends and whatever they connect to also

 

[London]

Larger battery may be able to spin the engine faster?

What does it do with the smaller battery? Spin and never starts or just won’t spin the engine at all?

Clean both of the battery cables at both ends and whatever they connect to also

Will try that thanks. Smaller battery completely dead no lights no starter but it is putting out 12.8v and is brand new

 

[85Hokie]

Have your battery load tested at local shop.
Sometimes a perfectly fine battery will quit for no reason.

 

[Thunder Fish]

Have your battery load tested at local shop.
Sometimes a perfectly fine battery will quit for no reason.

Yes,just had a 3 month old one die out on me,it wasn't due to store having it to long.