I think you could make an external power connector using a 9v battery connector. You would plug it into one of the three existing battery connectors. This is based on my recollection that the three 9v's in the AERCO are wired in parallel, but I could be mistaken. Ask Jerry. And don't mess up the polarity
Remember to wire the 9V battery connector with opposite polarity to how it would normally used (red wire negative, black positive), as it will be taking the place of the the battery output terminals, rather than acting as the opposite gender equipment power input. I made cables like this for two CA-UGLY preamps to run them for an entire multi day festival on one DVD battery, avoiding the need to change batteries.
Low-Discharge Imedion 9v NiMH rechargable batteries are the shit. [snip]
I bought 10 9.6v batts about 2.5 years ago for use with Nbox / Reutelhuber devices and have probably run them through 150-200 cycles with no issues. Of the ten, one of them has started to warp a bit, so it's retired, but the rest are still going strong. This is interesting because the Nbox will discharge these to below 1v, which is supposedly horrible treatment for NiMH devices, but they always seem to bounce back.
Watch them as they're probably about due for replacement. Do so before they die during a recording. My original set of Maha 9.6V batteries eventually died right around that age, after approximately that many cycles, and when they did I screwed up a few recordings before realizing what was going on. I was checking voltage before and after use and they measured fine, yet I started getting 'low supply voltage' type distortion in the preamps halfway through shows. Problem was that the batteries would recover enough afterwards to measure like a 'good' although discharged cells (say 7-8V) but under-load in the device they were dropping to something like 4V or less very quickly. Moral of the story is to measure Voltage immediately after use while the battery is still in the device to determine it's true, sustainable 'under-load' voltage. Without a load across the battery, or measuring after use, you risk a misleading reading.
No further problems after I realized that and I caught and replaced the second set just as they were beginning to die around the ~3yr old mark before loosing a recording. By then Maha was making the LSD version of the 9.6V (black/grey case) which also had a higher mAhr rating and that second set lasted longer and retained their charge longer than the original (white case) non-LSD 9.6Vs.
I had one of the original 9.6Vs balloon out all warped and misshapen, called Thomas Distributing to order another, and they immediately shipped a replacement free of charge.