Could someone recommend a supplier of Lithium ion battery packs (say 12V 5Ah or thereabouts). I've seen so many dodgy ones that I don't know which suppliers to trust any more!

 

https://www.maxamps.com/products/18650-battery-lithium-rechargeable

 

We have recently upped from our 12V batteries to the Swit S-8073N (14.4V/73Wh, 5.1Ah)

It's a little higher in voltage, but we needed documention for travel which our custom made ones didn't have