There's two sides to it. For peak loads and shorter routes measured in minutes or hours with easy charging possibilities batteries have been coming for 5-7 years now. The issue is charging since no regen is possible except load smoothing due to operating current engines at a higher thermal efficiency. It's an industry that only looks at cost and barely makes money, efficiency and low-cost workers has been the name of the game for decades.

The hard thing is the sustained loads over weeks. It's not like a car where it gets rolling and then keeps rolling with some air resistance, you need to constantly force yourself through the water, even though it is efficient on a per ton basis.

Consumption on larger vessels can be 150-300 tons per day, say 40 MJ/kg of energy content. Say you only need 50% due to earlier thermal efficiency losses. For a 3 week range from China to the US west coast you still need 30 GWh, or 300 000 Tesla 100 kWh batteries. Which is actually quite similar to the battery capacity of all Teslas delivered in a year. Using 246 Wh/kg we get that the ship needs about 120 000 tons of batteries. A 400m container ship has 140 000 tons of usable capacity, i.e. just the steel excluding all cargo and provision, so it really doesn't add up yet. Need a magnitude improvement before it can start making sense, and this is a calculation without even margins or considering for example China to US East Coast.

It's just incredible how energy dense fossil fuels are. Shipping and aviation will probably end up as the last industries to go green, because they actually use the energy density.