Using 200Ah cells or 400 Ah cells works well, but you need to make sure that the connections are done correctly.
When using more than one cell to reach the desired capacity, then you have to connect the smaller cells in parallel first and then connect them to the desired battery
voltage. Never make two 24V-200Ah batteries and then connect them in parallel.
Keeping the individual cell voltages between 2.9 and 3.5 V (May vary slightly with manufacturer) is the key to a long life. Making two separate batteries of 24V200Ah each gives you 16 individual cell voltages to monitor
. Making one battery
with cells paralleled first gives you 8 cell voltages to deal with. You just halved the potential points of failure. Also, when in parallel you get a chance to have a strong cell help a weak cell and even things out.
Most importantly, never charge to absolutely full (3.8-4.0V per cell) and never discharge to absolutely empty (below 2.8V). All these voltages are under a conservative loads as usual in house bank applications. That means about 20-200 A from your 400 Ah battery.
A number of real application tests by users here on CF have shown that for a 12V battery 13.8 V charge is safe and gets you to +95% full. The good thing is that these batteries do not have to be fully charged ever to enjoy a long life, as lead acid have to on a very regular basis. LiFePo like it better to hang around the middle.
Hope this helps.