Congratulations on reaching the big 70.
Why don't you just buy one of these power banks - I have a smaller version of an Anker battery, which is an excellent brand. This higher capacity version should genuinely last you 48 hours.
If you bought a blue tooth key board and combine it with your phone, you could then use your phone as a PC when your lap top dies.
Then you really could go a full 48 hours of constant use on the go.