The original pre 2018 Petzl Duo is the outstanding low-mid cost caving lamp. The release of the new Petzl Duo Z and S models has done nothing to change this from a cavers perspective.
With a suitable LED upgrade, and decent quality low self discharge NiMh batteries, the original Petzl Duo is without doubt the best mid range caving lamp available.
The original Duo was designed specifically for caving, and consequently knocks the socks off even the best of the low cost general purpose headlamps, on every level. Well not quite! Whilst extremely robust, in their original form they lack the output of many modern LED headlamps. However, with CustomDUO LED upgrades to suit most budgets, you will have a high quality caving lamp that is more reliable, versatile and suitable for purpose than any low cost, high output, general recreational headlamp, including the latest non upgradeable Duo models.
Original Duos (Modu'led 5 LED version, elastic headband) are available new online from £65 (UK) and can be easily modified to the more expensive helmet mounting 'fixo' specification, as outlined below. The original Duo in helmet mounting 'fixo' specification is a more expensive, and increasingly difficult to source, option preferable to cavers.
Having removed Duo headband, cut away 3 off strap holders on battery box. Small wire snips work well.
Trim back the grey plastic headband mount on back of lamp.
A bit more. Almost done !
Until it looks like this.
Spend a few seconds fitting one of our lovely upgrade modules, obviously.
Download Petzl helmet drilling template, link below. Print it out and double check dimensions (as it printed out at wrong scale for us). Now just ignore the template anyway, use your initiative and make sure you get the holes positioned correctly (especially on battery box).
The cable can be routed inside of the helmet. The headset or battery box can be threaded between the inside of the helmet and the cradle, and the cable simply looped under the bottom lip of the helmet, at the front and back.
There is no need to drill entry / exit holes in the helmet for the cable, no need to cut and rejoin the Duo cable, and no need to detach Duo cable at battery box or headset. Do not try as this is borderline impossible, and even if successful, the lamp is unlikely to ever be quite right again.