Rotate your battery usage and charge them in the laptop when there is a power outlet available.
I buy spare batteries for my laptop.
Depending on the length of the trip and the potential lack of adequate AC outlets, I might bring two fully charged spares.
I had a battery charger from Lenovo that could charge two spares at once. Plug them in overnight along with the laptop and you are always good to go. I used to be able to "hot swap" the lenovo batteries while the laptop ran on ac. That was sweet.
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