You could use a basic computer UPS. We do also offer the safety connector 6105.500, to this you add your own battery and charger. We do it this way as shipping batteries is very expensive and this adds some advantages in being able to change the battery and use a solar panel for charging if you wished to do so. The basics would be a 8aH SLA battery from batteries plus for example, this is like what is in a Power Wheels or your alarm back up, it cannot spill acid as it is in a gel and sealed. You also would need a suitable trickle charger of .5-1 amp. Such a set up could run a 6205 for about 5 hours. A bigger battery would extend the time and you can generally find up to 32aH readily at a battery store.