Backup Batteries is one of the achievements in Into the Breach.
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This achievement can be done in conjunction with the Rusting Hulks squad, as they have a similar Overpowered achievement.
It's possible to get this achievement by completing objectives that reward Grid Power, accepting +2 Grid Power as the bonus reward (or +4 in Unfair difficulty), and then spending the remaining difference of reputation on Grid Power.
Additionally, it's possible to spend 10 reputation (or less pending the difference needed) on Grid Power to get the achievement, and then undo the reputation spent; since the achievement is awarded as soon as 10 Grid Power is earned in a single island, the player will still keep the achievement after selecting "undo all."