If you want to install the battery in the seat post of Shimano's Di2 groupset, you firstly need the round battery and secondly a suitable seat post. These have a mount for the battery and offer a snap ring to ensure that the power supply remains in place. Surprisingly, alternative methods such as construction foam also work. Wrapping the battery with a bicycle tube and inserting this combo into the seat post - this also works surprisingly well and is also inexpensive.

A more professional way of mounting the battery in the seatpost has been devised by the southern German lightweight manufacturer Tune. The noble helper is called Energieträger and consists of two aluminum plates, two screws and a silicone ring. At around 8 grams, the energy carrier weighs very little and installation is extremely simple: attach it to the battery, slide the battery into the seatpost, tighten the screws lightly - done.

The battery holder only touches the seatpost with the silicone ring, so it leaves no marks. The technology is based on Tune's GumGum headset clamp. The clever part costs 19.90 euros and is available for diameters of 27.2, 30.9 and 31.6 millimetres. As is typical for Tune, the energy carrier weighs a mere 8 or 10 grams.