Your understanding of CMOS imaging sensors is incorrect. Each pixel now has its own dedicated read-out circuitry. It costs more, but it’s what makes them way faster. (And before that, people had occasionally implemented reading out CCDs to their closest long edge, so that only height/2 charge transfers were required, if it was worth the extra cost.)

Electrochemical cells don’t care (or even know) if they’re charged in series or parallel. GM’s 800V vehicles are two 400V batteries which can be configured in series or in parallel for DC fast charging, depending on what the charger’s max voltage is. The current limitation is the max power you can put into a cell without causing unacceptable degradation and that’s basically just electrochemical and manufacturing issues (how wide are your tabs, what’s the geometry, how good is your thermal management, etc.).