Magic mouse disconnecting for a few seconds, pretty often

There are many posts about this. First thing I suggest is a smc and pram reset.

Also look at this discussion:

Magic Mouse keeps disconnecting from bluetooth

particularly around page 6.

Basically you may need to insert a small piece of aluminum foil into the battery compartment to keep them from moving around (or possibly a piece of paper to wedge them in).

You don't say what kind of mac you have. If it is a mac pro you might want to look over this discussion:

Poor Bluetooth reception and jerky mouse

Finally google search "magic mouse loses connection". Your problem is not unque.

Don't know what rechargeables you are (were) using by I've been using my Sanyo Eneloops from the very first time I got my MM and have had no problems at all.

If the rechargables were shorter than the others, then that's most likely the problem.

More often than not its because you're using batteries which have a very small bump on the + terminal which causes contact problems, EveryReady Super Heavy Duty are a common culprit. Try switching to Energiser and see if this helps.