Jet fuel has the advantage that it is consumed as you fly. Some planes can start with full tanks, but not land. If they need to do an emergency landing, they have to dump the fuel. I imagine that would be difficult with batteries.
I think building battery cells designed to fail safely in an accident is probably a more reasonable option than trying to dump them.
This is why, time permitting, planes will first burn off or drop fuel before doing an unplanned landing.
They _can_ land fully loaded but you are exceeding the maximum weight for landing which is neither advised by the manufacturer nor is it guaranteed that nothing will break. So if you it‘s not an emergency that requires immediate landing, you won‘t go for it.
1) Detaching heavy objects while in-flight is a tried and tested technology. We've been doing it ever since flight was invented. 2) UAVs are not making the news anymore and fully autonomous landing has been commercially available since the mid-60s, granted, for very different type of aircraft, but it's becoming more common for light aircraft too.
Dropping UAVs from airplanes is of course a whole different ball game, but wouldn't you say it's.. doable? Ultimately whether the added complexity is worth it depends on the proportion of energy used during taxi, takeoff and climbing compared to the total which varies wildly depending on distance and other factors, but tends to be highest for very short (but also very long) flights which is where electric aircraft currently stand a chance.
If so catapults like aircraft carriers maybe a good idea.
Or extension cords that pop out when it gets airborne?