What do you mean, either by "fit" or "in parallel"? For fit, the original nicd cell is a standard size with two legs soldered in to the motherboard. The replacement nicd or nimh are the same size. The same two legs fit in the same place the same way.
And there is no issue of mixing different types in parallel. The internal battery is on it's own charging circuit. It doesn't matter what kinds of batteries you put in the 4xAA external battery compartment. They can be anything. Or were you talking about putting a 3xAA nimh pack in the external battery compartment and then needing a 4th to add to it or something? If you wanted to use a 3cell pack internally in place of the original style, there is no fitting, you just solder the wire leads. You'd have to just stick it somewhere with double sided foam or hot-glue, and there is plenty of room for that. -- bkw On Jun 4, 2017 5:53 PM, "user evers" <[email protected]> wrote: I can't help but wonder if there is not a cordless phone battery pack that might actually fit. I know there are ones that use (3) AAA cells and others that use what appears to be 2/3 "AA". The diameter to work with is 15mm or less. These are all NiMH from what I have looked at. I did order a new CMOS NiMH 3.6vdc pack for $6... I'll do some testing here once it arrives. The idea of putting NiMH or NiCad in parallel is not all that appealing.
