Must also not lose track that 200 Ah of 6-Volt is the same as 100 Ah of 12-Volt.
Amp-hours is NOT a measure of energy, and therefore leads to a lot of confusion. The better system is to measure energy in kWh (kilowatt-hours) which is the way electric cars and home electric bills are done because it’s an actual unit of energy. Fortunately a few large RV lithium battery banks are adopting the correct method, but many individual batteries are still sold by Amp-hours.