I've got a cheapish NiMH charger with LCD that tells me Ah reached when charged. If you have one of those it would be worth cycling each of them at least twice and record the results. The Cells are Panasonic HHR650D (from ES
Prius NHW10 (MK1) Hybrids - How to test and resurrect th
So a 6.5Ah NiMH cell (D size) is often fast charged with a burping action to absorb the gassing action at the electrodes.
So if you can only charge them with a constant current then charging them at the 10 hour rate of 650mA with some extra would be on the safe side but slow.
You may find more cells with low capacity after you have done the 2 charge/discharge cycles.
As you may have noticed when there is a dead cell in the string when you have current passing through the string the faulty cell is a resistor and has a negative voltage drop (V=I.R).
(If you just want to get it going for RWC and rego I wonder if you shorted the dead cells with links, and cleared the error codes that the BMS system may not detect the missing cell +voltage.)
If you can't get a hold of
Prius Spec battery would you consider another brand of NiMh cell with a capacity of at least 6.5Ah?
As the cells are 33mm to 36mm Dia and 60mm long two of them are 120mm and nominally 2.4V but when charging their voltage raises to 1.6V. So two would be 3.2V. You might get where I'm heading. Has any one replaced the all the cells with Headway 38120P 8Ahr cells. If the cells could fit. I Noticed
Coulombs post in How to Convert a Hybrid other cells like LifeBat may fit too.
Refd: from above link: Battery capacity in the 1997-2000 Japan Prius is 6,0Ah @ 288V (25-30 mOhm) NHW10 Not released into US market
The heating issues of NiMH during charge and discharge may be negligible with LiFePO4 chemistry.
But the per Cell BMS issue is there so until they include a magical 3.9V Zener that can cope with 10A bypass during recharge.
Or a smart BMS for $1 per cell.
I must check on what causes the venting and crystal growth on the dud cells. Is it Heat during overcharge or heat during forced current when discharged.
It would be very helpful to know what the MAX charge voltage is in the NWH10 Prius Mk1before it detects fault.