|It could be useful to utilise the plug, lead and semiconductor assembly of the old battery pack.|
If the battery pack has leaked electrolyte then take care when handling as the effusion is corrosive and presents a hazard for skin and eyes and should not be ingested.
Note: When preparing ends for soldering (points W,X,Y and Z) it is more effective to allow sufficient length for curling the ends into loops or spirals, somewhat larger in the case of points X and Z at the negative battery ends. This will ensure a stronger joint, more quickly made with less build up of heat in the battery.
Cut the 0V line close to the negative end of the lower left battery (point Z in diagram) and re-prepare the end for soldering later - strip, clean, loop and tin.
The diode (D1) is usually attached by a short length of wire, the wire having been soldered to the battery first (high heat) and then to the diode (less heat), this to prevent overheating and destruction of the diode. Thus it is best to separate the diode from the wire, rather than the wire from the battery. This should be a quick operation with a soldering iron, preventing heat damage to the diode.
In order to keep the two batteries, between points Z and Y, in line and ensure permanent contact between them it is useful to construct a tight fitting tube from about 160g/m2 card or fire-retardant material if preferred, by wrapping tightly around batteries and securing with tape. The tape I find useful here is that white masking tape commonly used when paint spraying.
For connecting points XY and point W to D1, short lengths of copper wire, single strand about 22 or 23 SWG (0.025 inch or 0.65mm), should be prepared with looped and tinned ends as mentioned previously.
Pre-tin all battery ends.
Solder wires at WXY and Z. Then solder wire attached at W to D1.
Arrange the flying leads and tape these and the WX battery to the tube containing the Z-Y batteries, conforming to the general arrangement in the diagram.
Before locating assembly into the space at left of the keyboard ensure that the two batteries (Z-Y) are making firm contact, a tight fitting tube will help to ensure this, and check output at PL8 using a multimeter.
An alternative method.
If all the above seems a bit 'hairy' then another solution would be to adapt a 4x AA battery holder of the type commonly available from Maplin, fitting the flying leads, plug and semi-conductors in a manner that maintains polarity as in the diagram above. This could be located in the space between the main PCB and the PSU.
This arrangement would certainly simplify replacing batteries at a later date, albeit at the increased risk of inserting batteries with polarity incorrect. Consider that another party may obtain the computer after you and may not be aware of the polarity issues. If this method is adopted it would be a good idea to clearly and permanently identify the + and - ends of the holder's individual cell locations.