I have a Racal Dust filter mask I use in my woodturning. It is a simple motor in a mask that blows a stream of fresh air through a filter. The product is no longer made but is still very serviceable but the rechargeable battery pack needs replacing.
The only information I have is as follows:
Racal product. Charger Input 240v 50 Hz Output 4.2v 230mA .96VA
The battery pack contains 3 X 5/4 Nicad rechargeable batteries of a size no longer obtainable ( my local branch Maplin's has searched for me) and it ran for 4 hrs.

There was an 8 hour offboard rechargeable battery pack available once, which had 3X 1/2D Nicad cells.

I want to make an 8 hour rechargeable battery pack connected by a lead to the mask which contains the motor. The connections are not a problem, I can change them as needed. Can I use the same charger?

Hope you can help. My local Maplins said they thought they could but were too busy when I went there

Sounds like motor 3.6 volts(3 [email protected] volts) Maybe you could outboard you own
3.6 volt battery. Would have extended usage. Can be as big a battery pack as you want, just not more than 3.6 volts, Then make sure charger has capacity of any increased size of battery pack.

Would something like this work:
Sharp CL250 3.6 Volt NiCad Cordless Phone Battery at Lowcostbatteries.com