I'd like to be able to do something similar, but the old batteries in these things seem like a point of catastrophic failure. How is that dealt with?
If it's an offsite backup, you would deal with it like you would any DR site-- either plan for yet another backup, or presume that it's unlikely that both the primary and replica would go down simultaneously and accept the risk.
Remove the batteries. Datacenters have redundant power and UPS.
If it's an offsite backup, you would deal with it like you would any DR site-- either plan for yet another backup, or presume that it's unlikely that both the primary and replica would go down simultaneously and accept the risk.