High charge batteries, I suspect are vented while '24hr' charge batteries are not. Clone batteries might not be suitable for persistant rapid charge. Also depends how often you use the machine. Do a google search on cells- plenty info there. Alternatively, you can 'build' your own if you can open the battery case.
Another thing to bear in mind is the charge rate. If your clone cells are rated at 1.3AH, charge rate will be 130mA and tricle at (once battery charged) 13mA. Now, if your charger is not an 'intelligent' charger and existing battery pack is rated at say 2AH, charger will put out 200mA to cells that max current should be 130mA. Heatr build up will be a problem then. Often a thermistor is included in the pack to sense the temperature rise that then starts to limit the charge current. If rated at same AH, then go for it, nothing to loose.
Advise would be, do you rely on your machine for work? If yes, get the proper set or look for dedicated cell stack that slots into your battery case (a german firm advertises such packs). I purchase such a unit for my Festo cordless. It has not let me down.
RS will sell you cells with tags, that can be used to make up battery packs.
