I use this battery Aukey 28000mah Multi-voltage External Battery Pack: Amazon.co.uk: Electronics with this cable Buwico® Power Charger Charging Laptop Adapter Cable: Amazon.co.uk: Electronics and get 15-20 hours mobile life from my SP4 (including the internal battery life)
I use this battery Aukey 28000mah Multi-voltage External Battery Pack: Amazon.co.uk: Electronics with this cable Buwico® Power Charger Charging Laptop Adapter Cable: Amazon.co.uk: Electronics and get 15-20 hours mobile life from my SP4 (including the internal battery life)
International airport security is widely refusing battery packs from checked or carry-on baggage, due to fire risk when the cabin is pressurized or if ambient temperature should change quickly.
This is a major factor limiting manufacturers from increasing battery capacity. They may exceed future regulation.
Here is a good pack I own, which is being refused already.
3rd party chargers? | Microsoft Surface Forums
Here are the current battery regulations in the USA:
Pack Safe – Lithium ion and lithium metal batteries, spare (uninstalled)