The 48w 10Ah battery has proven to be a good fit for commuting, shopping & touring for the Long Haul Trucker e-bike build.
For most commuting & shopping trips, the small battery works well for these 35 mile or less trips. The battery isn't bulky or heavy. It's efficient and easier not to ride with a huge battery. I believe the bicycle actually looks better as well.
After the testing, I purchased the same 48w 10Ah battery battery for touring. The additional battery can be:
-carried beside the other battery on the rear rack
-carried in a rear pannier.
-carried in a front pannier.
This has the advantage of controlling the weight distribution on the bicycle when touring. In case of battery failure (which I've never had happen) it's always an advantage to have two batteries.
For commuting or errands, the batteries can be alternatively used.