Unused for 5 years BR1500G - Flashing Battery (can't get connection)

[Anonymous user]

Hi, so, I had a BR1500G stored well for 5 years (not bumped around, stable temperatures, battery in shipping orientation until today, etc.) and came across to open only today. No startup sequence, just went straight to double beep every few seconds with a flashing empty battery charge. I found out later this means there is no connection. I inspected the spades and the female side and it looks okay, like it does physically connect but have my doubts because ONE of the attempts at plugging into different wall sockets, I got a ceaseless beep with a F04 error (Clamp Short). Aside from that, it's been the same story with double beep flashing empty battery charge/no connection. 

Earlier I had it plugged in for 8+hours with no change and have tried a power cycle a couple times after. I'm not too familiar with this model or battery but maybe I can take a picture because I probably can't explain it well; the side brace of the battery does not sit flush inside the unit and there is no discernible click or anything telling me it's seated properly. Of course I have my green sticker side up and inserted properly so I'm not confident in the battery installation but I also don't want to just jam the battery down with force since I heard that may mess up the spades.

I'm not an expert on how long a dormant battery would last but either the battery is totally dead though I would have thought I'd at least get a replace battery icon (which has not appeared), OR, I need to let it charge over 24 hours+ to even see a change in the battery charge level. That single instance of F04 did make me think maybe the connectors are off though and that the one attempt with F04 result happened to receive some kind of connection, albeit not secure I guess.

I have a time-sensitive unique workload that needs backup peace-of-mind and I've had two power outages this month already (that's what prompted me to go get the unit which has been in a different house until now) so I'm in a pickle! Thank you so much for your help and I will of course come back here and reply if it turns out it really needed a long wait to charge or I manage to get a stable consistent connection somehow. Either way I'll be back, thanks!