So part of the answer probably depends a lot on how many batteries you need to charge and what kind of voltage you're looking at.

For example, I have a battery pack that uses 10 x 2100mAh Imedion AA batteries. By using 3 seperate MAHA chargers simultaneously at a 1A charge rate - I'm done in 2 hours. OK for the house but not exactly a collection I'd like to take touring. The chargers are, combined, 10x the size of the battery pack. Using a single portable charger on the road would take me about 10 hours to do the same thing. Less time with a fast charger, but better have spare batteries as a backup, because those are hard on batteries.

On the other hand a 6,600mAh 3S1P Lipo pack with a 4C charge rating will take a 26.4A charge rate and can be safely charged in about 15 minutes. Again - the chager is larger than the battery, but much more compact than three MAHA's. Alternatively a 2A charger is half the size of the battery and can simply be used to top up the battery when convenient rather than waiting till its absolutely necessary. Thats what I'd travel with.

The extra battery capacity makes emergency charging less likely so a larger battery and smaller charger works out better for me on the road. It's still not much bigger than an iPhone.