Leaking battery Bike wouldn't start after 6 months standing in garage. Couldn't recharge battery, bought a new one, still wouldn't start. Tried charging the new battery which started leaking. Shop gave me a replacement battery which has been fine for a couple of months until I got the bike out this morning and it wouldn't start. I took the battery out to recharge it (even though the bike has only been left a few weeks) and it was sitting in a pool of liquid (assume acid!). Original battery was Yuasa YT12B-BS replaced with CT12B-4. Have I got the wrong battery?

Yuasa batteries are expensive but with good reason. They are extremely high quality and follow the old adage 'you get what you pay for'.
Cheap batteries appear initial good 'value' but the extra investment will pay dividends long-term, if properly maintained, your Yuasa will last many years.

If you suspect the liquid is acid, neutralize it with some baking soda just to be sure. You don't want that dripping onto anything metal or pain, causing damage.
Once you have it neutralized, wash it out with water.

It sounds like you ride infrequently and bike may have periods of serveral weeks on occasion without being ridden.

My recommendation would be to install a quality replacement (like the OEM Yuasa) then purchase a battery maintainer that you can plug in while bike is not being used. Good maintainers are Optimate and Battery Tender. (I have both myself - I really like the Optimate 4.) Both of these come with a waterproof 'pigtail' harness that you can permanently connect to the battery - then when you put the bike away, you can simply connect up to it without having to remove anything.

Hope this is helpful.

Good Luck!!