MV-1 boards; black screens & backup ram error

I recently bought alot of 4 cabs and 3 boards from an arcade dealer. All of the boards are MV-1 one slot boards, and all three of them don't work.

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The first one, serial #132745 was mounted in a cab. Cab power supply was shot, it didn't output anything to the 12v or 5v, so I replaced it. Now boots to a black screen with or without a cart inserted. Tried booting with/without a cart with dip 1 on, still nothing. Didn't get a chance to test the battery voltage.

Next one, serial #140284, does the same as the previous. Only difference is that every now and then you can hear a pop or scratch come from the speakers. Battery voltage reads around 1.5v. This board was loose and was not in a cab.

The last one, serial #356990, boots to a backup ram error screen, with or without cart.

Address 00D00000
Write 5555
Read 5AF6

Tried booting with dip one on, no change. Battery voltage is .5 volts. This board was loose also and was not in a cab.

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I haven't tried turning on all 8 dips for any of the boards, although I'll do this the next chance I get. Also, I have no idea how long any of the boards have sat without being powered on, and I didn't think to leave the units to possibly recharge the batteries.

Any ideas for a simple fix on these, or any suggestions for people/businesses to contact that would repair the boards? I hate to toss them, but if it's cheaper to buy another board I'll just cut my losses.

You can remove the batteries, they have had it, they only back up the soft dip settings. Its unusual to boot to a black screen without an error or the cross hatch pattern which you will get with no cart inserted on a working board.
Where these bought as working boards or "as is" lot.

They were bought as is.

Where can I find replacement batteries that would work properly?

dont worry about the batteries, they do not effect the boards boot up.
Just snip them out