Does such a thing exist? A nice tidy solution to mount my light battery to the frame? Rather than velcro / zip tie to frame.

Put the battery in a tool bottle that fits in a standard cage?

http://www.decathlon.co.uk/tool-storage-bottle-500-ml-id_8123841.html?

That might do the job, I’ll just drill a hole in the top. Bargain price to, cheers.

If you want something more bespoke for a particular light then MTB Batteries can make one up for you. There is a pic of a water bottle battery on their site: http://www.mtbbatteries.co.uk/mountain-bike-batteries/

That is a bit sexier, I might drop them an email and get a price. Cheers

Just make one out of an old water bottle that has a wide opening.

Cut the gubbins out of the back of the spout on the lid’s underside. The spout pops out leaving a hole which the connector will now fit through.

Cut the spout in half lengthways/vertically. The two halves can now be slotted back in place around the wire giving a nice seal around it – better than drilling a hole in a tool caddy lid

works well in a bottle . Drill through the spot from the inside and you can thread a battery cable through my frame like strapping it does.

https://goo.gl/photos/tXufuHJ64ZSNEFSy8

I just bastardised an old 500ml bottle. Popped the battery in, cut a slit in the nozzle to get the cable through and screwed it back together. I did have to gaffer tape the outside of the bottle as I had to split it to get a 6 cell battery in. Been like that for a couple of winters now, much easier and less faffing than a battery bag.

My MTB batteries bottle cage battery is a tidy and reliable thing that with a zip tie or two stays put and doesn’t rub my frame

I though about bottles for ages but then bought one of those “triathlon feed bag” kind of things – this one.

It works well, I can slip in some sweets too and still use my bottle cage for water.