As many as 10 in the winter. 12 if I rode my touring bike which I don't generally do in the cold anymore, my mountain bike / fat bike don't have wireless sensors. I don't bother with an HR monitor anymore, so that would have been an additional 1 in the past. To count individual cells add an additional AAA for my tail light and 10 more 18650s for my 2 6 cell headlight batteries.
- GPS
- Phone
- Camera
- Headlight
- Helmet light
- Tail light
- Left boot heater
- Right boot heater
- Heated gloves (I'm down to a single battery to power both through the use of extension cables)