Which battery

I cant tell you which battery number but I can recommend  the BOM battery which came with a bike I bought years ago.  The bike has been out of action for most of the time but the battery has an uncanny ability to retain its charge .I just check it once a year and give it an hour on trickle charge which I probably does not need. And I just thought it was just sales hype.

The BOM battery is a sealed unit of 3 cells  that you have to conceal within an old  (or new pattern) battery case.  Mine came with a 500 cc Rudge !.Google BOM battery.

I have a '57 ES2 which is has a panier style battery box, so there for there is no reason to " concel the battery in an old case", I use a B38-6A which now may be available as AGM [sealed] and is 6 volt 14 amp hour.

BOM 'battery' this is a company selling all sorts of batteries. IE there is no such thing as a BOm battery. So we are no wiser, what type of battery is it Robert T?

Looks like 3 torch  batteries side by side encased in black plastic with a flat top covering all 3 cells  ,flat tag connectors that I don't like much. I have at least half a dozen other batteries in use ,but none stay charged like this one. I can understand your frustration as I am also finding it difficult to trace, The Co website is useless. Perhaps like all things that seem to last forever ,Its not a good business plan.Appears to have come from Burlen Fuel systems in 2014  made in the USA.

That sounds like the Cyclon battery, one version is 3 cells in a row.

I think you are right John, A re-branded Cyclon, apparently lead acid with an unusual spiral plate construction , which I imagine would make it extra strong . All I know is its 6 years old and I would confidently leave it all year and then find it needs no charge,wheras   all the others need topping up.every 3months or so. If it were normal battery shape and with the bolt on terminals it would be ideal. Only 5ah capacity.Its use on the Rudge is for lights only ,and as I have no intention of riding that beast at night It will probably outlast me. The only batteries I have had with  similar behaviour is the Silver Hydried ? ones that come with an Eberspacher  equiped telecom ford transit, 16 years on with no maintenance and still perfect.

Yes these do maintain a charge for a long time. But there is one big disadvantage using these batteries on British motorcycles. The batteries have a charge characteristic that is VOLTAGE dependant. If you have a decent controlled charge voltage-electronic dynamo regulator or even alternator regulator/rectifier then there is every chance you will keep the cyclon battery safe.

If you have the original 6V alternator switching (PRS8) system then you will cook these batteries after a 50 mile journey.

With ALL batteries being used different to the original (lead acid) I recommend checking the battery charge characteristic and make sure your bike is within that specification.

Thanks for the tip Alan.  At last a 6v battery with a capacity around the same as the original Lucas!  14Ah is good and better than the gel and Cyclon batteries which, as Al Oz, says are sensitive to charging rates anyway, so that could negate the slow discharge benefit.  I'm sticking with  the PRS8 switch as I have several of them!  

The B38-6A are on eBay as Yuasa or Lucas for around £38, although some sellers won't send them with acid.  With long term disuse all you need is a decent "conditioning" type of battery charger (I have two different models) so you can keep it topped up.

Now all I need is to find a period-styled battery box that's not as expensive as the battery!  Or - as The Rolling Stones famously said - "Paint It Black"!

Stay safe!

Time and again I see LUCAS mentioned in text. Please be aware the real LUCAS died in the mid 1980s. What we have now is products made under licence mostly in the far East and sold in a green box. Mostly the company that sells them does not have any technical backup.

Yes Al, I think most of us know that "Lucas" is foreign, but so is most stuff we buy if it's electronic.  It happens throughout industry and commerce.  Rarely are "old names" still run by the original companies.  The Lucas batteries on this post are probably Japanese Yuasa, although they also have 'connections' with China and India.