I’m a bit confused, I’m still using an FM Futaba 7c system with a FP-R1270F receiver, not that I think that matters. I have some new batteries used in telephones, these are 1.5v. I packaged up four of them and get a full charge around 5.5v.. The system came with a 4.8v battery pack, I was wondering if this would work or better yet I have lipo battery packs of 7.2v. Would the higher voltage burn the receiver out?

A quick note to remember is that the 4.8 volt pack is the "nominal" voltage at 1.2 volts per cell. A fully charged pack will reach about 1.4 volts per cell and top off around 5.6 volts. The same goes for a 7.2 volt lipoly. That voltage is for the normal voltage, however, fully charged lipoly cells reach 4 volts each and you would be putting 8 volts to your RX - that is too much.

So, the simple solution I use: The max I go is a 5-cell RX pack (6-volt) that will max out about 7 volts. or if using Lipoly for the RX, install a regulator.

Please note, you are talking to an Old JR radio guy who stil prefers using 4.8 volt NiCd's in his planes

Generally speaking...servos are more sensitive to higher than recommended voltage than receivers.

Sometimes, you will notice servos twitching or spasming when you first switch on a 5 cell NiCd or NiMh pack that's fresh off the charger. (talking about 72 mhz stuff here )

A point not covered so far is that you what a RX pack capable of at least 600MAH. Your telephone batteries are not going to supply that capability even ganging them together fora usable voltage. A NIMH pack of 2300MAH @4.8 Volts is a good, inexpensive Choice. I've bought them for as low as $10 each delivered. 1000 MAH Nicads or greater is needed if you are going to do more than a couple flights a day.

Another point is chargers. IMHO, a good peak detection charger is a must, one that will charge the type battery you have. This is really important for NIMH as an over charge wild toast the pack. Idid that with my first one for my 9C TX. Charged it and flew it for a couple flights. Got home and "topped it off"on the wall wart over night, didn't get to the field the next day so Ileft it on the charger. The next day was a fly day and about three minutes into the first flight the low battery alarm went off on the TX. Luckily Igot the plane down. Checking the pack showed two cells gone, so my 8 cell pack was down to a 6 cell.

With Nicads you can leave them on the trickle charger for a few days without fear of killing them, but you are never sure how full the tank its, so a good peak charger solves that issue quite nicely.

Batteries have cost me a plane and almost a second. Short cuts and salvage batteries are just not worth it. If a battery starts giving a problem, in the recycle bin it goes. Saving a couple bucks on a battery to loose a few hundred wrapped up in a plane just isn't a good trade.

Don

Even taking into account your questionable choice of radios your advice on batteries and voltages is solid.

most receivers can handle up to 9 volts, servos are usually the limiting factor

*edit i called horizon hobbies about this while back, the receivers in question were the 649 and the 955

The post that said the capacity of the battery is questionable is correct. When making battery packs you must know the capacity.
If you're flying a basic 4 or 5 servo aircraft, then a 4.8V 600 mAh battery will be good for 3 or 4 flights.
If your flying an aircraft with 7 or 8 servos then you need more capacity, I have an aircraft with a 2700mAh battery, still with 4.8V as I had 2 retract servos that were rated for 4.8V only.
I use 6.0V packs on most of my other airplanes, some NiCad, some NiMhid. They indeed but out around 7.2V fully charged right off the charger.
Any voltages over 6V I use a regulator. I figure that is a lot cheaper than a new receiver.