Giving them the ability to self-charge energy weapons doesn't seem unrealistic; in fact non-nuclear tanks could incorporate a larger alternator and just burn fuel to recharge their lasers.
IRL the M1 Abrams tank's propulsion generates 1.12 MW mechanical. Assuming a 99% efficient alternator and a 99% efficient graphene ultracapacitor or CNT compulsator, you'd get a charge rate of over 1 MW.
(A crappy 90% efficient alternator you find in IRL junkyards and a 85% efficient last-generation battery gives a effective charge rate of 856 kw, but I dunno how energy weapons would be viable with last/current electrical batteries, so we'll assume something at least halfway; 95% efficiency per stage)
I do you one better :)
If you got a Electrical Transmission that means you already have the generator right there.
Diesel/Electrical propulsion was very common in WW2, for submarines. Indeed the Electrical Transmission of the Panzer VIII Maus could be used as a generator. The "plan" for getting them across rivers was (they were way to heavy for bridges):
One the shore, operates as generator
One driving along the bottom of the river using a snorkel for the crew, powered via cable by the one on the shore.
When both are at opposing sides of the river, just swap the generator and d(r)iver around.
The M1 Abrams, other modern tanks and the average Airplane (passenger liner included) come with a Auxiliary Power Unit - a simple Motor/Generator combination - for powering all the non-propulsion systems.
It is not tied to the main engine(s), because it could be problematic to have the engines running just to have power (Tanks) or all engines might fail (Airplane), at wich point you need a seperate generator.
But that does not nessesarily mean you do get to use it to recover energy based ammo:
You do not just need enough energy to fire a laser or railgun, but enough energy density.
And it is possible that whatever you use to store the energy in, can only be restored using industrial grade power generation (easy to provide by the power grid, hard to provide even by a huge group of tanks).
Take the Aluminion-Air battery. It is technically only a battery. But you can replace - and then recycle - the Aluminium Electrodes. So it is a sort-off recharable battery. So it is actually in the consideration for electrical cars, given the easy to replace and then "recharge" the electrodes for use in another vehicle.
And depending on the process, cutting the energy you have by a factor 1000 does not increase the time for the recharge by 1000 - but might make the recharge entirely impossible.
< Message edited by zgrssd -- 3/6/2021 10:14:07 AM >