It's a lithium battery that was soldered to the board. Similar to the original Just a Lithium type. I'm going to change it to a coordless battery. Would you happen to know what type of connector to use as I would like to change it with the game on and lose the scores or calibration.
I think if you use a lithium battery you have to add a blocking diode as well or the game will try to charge the lithium battery and that won't be good.
I have no idea whether your game has the blocking diode or not. But if you want to go to a cordless phone battery then you'd need to make sure that it does NOT have the blocking diode or your battery will never charge with the game on.
Regarding the connector, I just unsoldered the leads that the original battery attached to and ran 2 wires down and away from the boards into a plastic tray I screwed to the side of the cab. Like this:
Then you have to match the plugs on the cordless phone battery with a male connector on the wires coming from the power board. I just checked; I don't have the package any more that had the connector I used. I matched it by taking my cordless phone battery to Fry's and going through their connectors until I found one that had the right connector on it that would mate with the battery connector.
Sorry, that may not help you much but that's how I did it.
I can confirm that you can 'hot swap' the cordless phone batteries with the game on once you've got the connectors in place. And that way you can save your high scores and calibration settings between battery swaps.
Oh, it's also a good idea to enclose the battery in a plastic baggie in case it leaks. And I replace mine every 3 years.
And if at all possible, charge the cordless phone battery to 100% before you put it in the game the first time. (I kept an old cordless phone that used NiCd batteries just for this purpose). By doing it this way I could keep the game off for 2 months or more and the battery kept the game going just fine.