18mm x 65mm dimensions Batteries usually LiPo (lithium battery) but also available as NiMH (Nickel Metal Hybrid). Basically a traditional cylindrical battery that is rechargeable and around 3.6v usually used in battery power packs for lights etc but also as individual batteries for torches etc.
I believe at Strathpuffer there will be some kind of stand operated by the sponsors where lights can be charged for a nominal fee.