Battery in battery operated HP-IL Thinkjet 2225B

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Dear all,

I am revitalising my HP collection and try to bring life to my battery operated HP-IL Thinkjet 2225B. It is fed by a dead rechargeble battery. I assume that it is also a 4.8 V battery, as it is charged by the same power supply as the batteries in the small thermal HP-IL printers and the digital tape drive. What I read in another thread was that the connection near the centre of these batteries is the positive one, and indeed, I used a DC power supply to feed the digital tape drive in this way.
However, the look of the battery of the Thinkjet is different. See picture in the attachment. Does anyone of you know if the middle connection in this battery is also the positive voltage one?

Thanks again for replying.

Henk Schellen