On new phones, how are two batteries at half capacity able to charge faster than one at full capacity?
When you split a certain capacity battery into two separate (half size, half capacity) batteries, you might be able to have better thermal performance.
That means, it gives you more flexibility in where the batteries are located and that could potentially help in keeping the batteries cool(er) during charging.
During very fast charging (maximum current you can get away with) batteries get hot. If you have two separate batteries it might be easier to spread that heat and/or you could charge only one battery at a time while the other one cools down.
Do realize that companies like Oppo prefer a short charging time over battery lifetime so they will employ all kinds of &quot;tricks&quot; to lower the charging time. That is their choice but realize that the faster charging increases the battery's temperature and that in turn increases wear on the battery. I would advise to charge the batteries slowly when possible and only when you really need it, charge them as fast as possible.