Hey all, I am wondering if someone with some more expertise can help me out here.

I recently acquired an Eaton 9130 with dead cells, unit untested and condition unknown and a broken fan. I replaced the fan with some light soldering and tinkering which fixed the noise problem. The next problem was the Critical Errors to try and clear out.

Today I purchased 4 new cells for the unit which are compatible with it. Thankfully the previous critical errors which came up are no longer are present.

The unit:

• Can detect the batteries
• Is charging the batteries
• Can display a run-time etc.

My problem:

• The unit is stuck in bypass-mode
• The unit when attempted to put in normal mode outputs the following event logs
• Go to normal mode
• AC Inverter OFF
• Go to bypass mode

I checked the rear of the unit and I see no wire or connection which might be causing the issue on the bypass patch. I followed the user manual and it doesn't match those conditions either.. but if I go into the panel > Control > Go to normal mode > Enter - The unit makes a 'tick' as I hear a relay but then ticks again within that 1 second - Putting itself back into bypass mode.

Here is what that looks like:

Unit running OK in bypass mode and charging batteries

But if I unplug the UPS from AC power it sits in stand-by mode and of course the equipment connected just shut off which isn't ideal.

This had me starting to think the AC component that handles this rail or 'step' in the chain is/was broken or a short somewhere is happening.. but if I unplug the unit and it goes into stand-by mode, if I press the power button for 3 seconds to "turn it on" it will actually power up and provide power to the equipment connected to it. With zero mains plugged in, fully self-sufficient from its own battery bank.

Here is what that looks like:

Battery power and AC functioning manually

So this is what has me perplexed. - Last pointer, I opened up the unit today again once everything was d/c'd and de-energized; just to go over the board/power components one more time I cannot see any obvious corrosion, blown capacitors or anything that stands out.

I made sure the primary positive batt. terminal was plugged in properly, it was OK as was the negative one.

Without a multimeter I can't probe or test anything but I am happy to buy one if that's all I can do in order to isolate what needs replacing/cleaning or whatever the case is - I am hoping someone on here can suggest something that will help a great deal- I'm not expecting miracles but it would be awesome to see this thing going in order to replace my 950VA vertical units.

Tldr: The unit functions/communicates OK, the unit charges OK, the unit can power from itself OK, the unit can power from mains OK, the unit bypasses OK, the unit's normal mode is NOT OK, the unit's transition from on-power to battery-power to prevent equipment power loss automatically is NOT OK.

At this stage this is my last hope before I feel like I've wasted some money, I am hoping with some brain power together we can solve this :)

Any help is appreciated!