CustomDUO v42 and Simple LED upgrade modules are very well suited for use with 3.7v li-ion batteries such as 18650s. In fact, better than from AAs, as the power density of 18650 Li-ion cells is greater and will realise the highest outputs from the LED modules for longer !!
IMPORTANT - 3.7v 18650 Li-ion batteries must be connected in parallel (or just one battery), so that the total voltage is 3.7v (approx 4.2v fully charged).
Batteries must not be connected in series, because total voltage (7.4v for two batteries in series) will be too much, and module will be damaged.
Extended run times can be achieved using e.g a v42 CustomDUO module with a 7000mAh 3.7v li-ion battery arrangement (2x18650 wired in parallel). This can be approximated as follows (remembering of course that module is thermally regulated on higher settings to protect LEDs from over temperature operation);
setting 1 (7000/150mA=) 45 hours
setting 2 (7000/700mA=) 9 hours
setting 3 (7000/350mA=) 19 hours
setting 4 (7000/1400mA=) 4 hours
CustomDuo LED modules are factory configured for use with 4xAA batteries (the normal Petzl Duo battery arrangement). The v42 battery charge indicator is therefore configured for this arrangement, showing 1-5 green LEDs to indicate battery charge level for 4xAA batteries (not 3.7v li-ion)
However, the latest Customduo V42 (r02) software features a 'cheat code' to calibrate the battery charge level indicator (1 to 5 green LEDs) for use with li-ion battery arrangements. Once the code is entered, a fully charged 3.7 li-ion battery, will show 5 green LEDs.
The battery charge indicator 'cheat code' is #3742# entered using the infrared remote control.
It is possible to repurpose the regular Petzl Duo battery box to accommodate li-ion batteries, but far from ideal !!. The batteries barely fit and the conversion can prove tricky. It is probably not for the faint hearted or technically challenged. Anyone considering this modification for the first time would be wise to use a sacrificial Duo, as it would be a shame to ruin a perfectly good lamp when things don't go to plan!
The basic procedure is to remove the cable from the battery box, and then gut the battery box by whatever means possible, in order to leave a clear shell that can accommodate e.g. 2x 18650 batteries (wired in parallel at 3.7v with suitable protection / battery management circuit). Two cells will fit into the battery box shell, but note that it is a super snug, arguably impractical fit, particulalry around the battery box lid.
A far better option would be to use a Lil' Monkey battery box, available with RH (right hand) cable gland, suitable for the Petzl Duo.
see Lil' Monkey battery boxes (these can be added to same shopping cart as Customduo modules etc)
The Duo lamp cable can be cut at the Duo battery box, fitted directly to the Nora battery box and connected up to a suitable li-ion battery pack with JST connectors.
The standard Nora box uses a 1s2p 18650 li-ion battery pack. A 7Ah pack will provide very good run times. Approx 20 hours on setting 3 using a Customduo v42 LED module.
Another neat, practical and light weight solution would be to fit Duo lamp head to an Edna2 Battery Box.
Also available at Lil' Monkey battery boxes
The Duo lamp cable can be cut at the Duo battery box, and the Duo cable then fitted directly to the Edna battery box and soldered to the PCB at the gland end of the box.
The Edna battery box uses a single 18650 li-ion battery, either protected or unprotected. A single 3500mAh 18650 battery would provide good run times. Approx 10 hours on setting 3 using a Customduo v42 LED module.
3.7v li-ion battery pack conversions can be easily and effectively charged with our 3.7v li-ion Nora switch mode battery chargers. See here