this is a nice idea but handholding alliances will just donate tower to each other - not gonna fly...
There are two additional factors - not mentioned in the OP - that seek to counteract this:
i) On capture, a certain percentage of stored energy is destroyed (most likely 10%, but can be adjusted by us easily)
ii) On capture, a certain percentage of energy is directly taken by the entity who captures the tower (most likely 10% as well, remains to be seen - we could also have this at 0% and set i) to 20% instead, for example)
Now, that of course does not mean that artificial "handovers" aren't possible. However, these artificial handovers only work if there is no real contender. After all, a rival might just want to take that tower towards the end of the season - he does not care what your handover plans are. The incentive for a real takeover are much much higher than anything that we have right now.
So as long as the stated design goal - generating significantly more real fights between top end groups - is met, we can live with the fact that sometimes towers are given away to try and game the system.