I am planning on maybe replacing the NiCd battery in the Futaba 7C 2.4Ghz transmitter I am going to purchase with a higher mah NiMh version
http://www.all-battery.com/index.asp...ROD&ProdID=166
in order to get longer flight days but I'm a little concerned about 100% compatibility.

Is this a good idea? It doesn't look like the same shape. Any cons?

Just a little worried about putting a different battery in a brand new $300 radio.

Thanks in advance.

G'day Mate,
If it's brand new, & you have not used it yet, how do you know it won't last a full day of flying.
If it's anything like my Spektrum DX7, it will last much longer than you need for a day's flying.
Try it & see first. Don't waste money if you don't need to.

I recently put that same pack in my Airtronics transmitter, works just fine.
Does your TX have the flat pack or square pack?

Not sure - don't have the radio yet. Why, does it matter? Just wondering.
Thanks.

A replacement battery has to fit in the battery compartment.
You linked a square pack, here is the flat pack that some Futaba radios use:
http://www.all-battery.com/index.asp...ROD&ProdID=513

Cool. Thanks. I'll be buying the receiver in the next couple weeks and will get the one that matches than.

Be aware using that pack does not neccessarily get that capacity out of the battery using the wall charger that comes with the radio. To get consistant full capacity charge those batterys are going to need a more capable charger.

You are trying so hard to get everything at once and many bad choices are hard to avoid. What till you actually are flying and many of your choices will change.

John

I have the Multiplex charger on my list http://www3.towerhobbies.com/cgi-bin...&I=LXKSY1&P=ML - that should give them a full charge, correct?

Thanks for the advice!

Yes that will do the job nicely. I use a pair of the english made Ripmax chargers which are the same as the multiplex.

It's not much. Just $15.99 US. http://www.all-battery.com/index.asp...ROD&ProdID=166

And it'll give me 2300 mah instead of probably like 600 mah in the stock batteries.

Cappa, your Tx doesn't use the flat pack, I checked for you.
Here is the battery your Tx will come with:
http://www3.towerhobbies.com/cgi-bin...?&I=LXLV15&P=V

So this is the proper replacement:
http://www.all-battery.com/index.asp...ROD&ProdID=166

The charger that comes with your radio will charge both replacement batteries (Tx and Rx) but it will take 21 hours for the initial charge (your wall wart charger is 150ma output). You can use your multiplex and do them one at a time, at C/10, for 14 hours each for the initial if you wish. The amount of energy you will use in a day will most likely be replaced in a good 12 charge with the wall wart, if you are flying again the next day. If it is not fully recharged in the 12 hours, you will still have PLENTY of juice to fly again, or you can peak each battery with your computer charger the morning of or at the field.

Again, I have the same capacity battery packs and use a wall wart for most of my charging, peaking the batteries once in a while with my computer charger. This works perfectly.

Edited: The wall wart charger that comes with the Futaba 7c radios has an output of 150ma Rx, and 170ma Tx. This would charge a 2300mah battery in 21 hours (2300x1.4/150=21)

Someone at the field yesterday said the 7C comes with 1000 mah batteries. If so maybe I won't upgrade for a while.

GaRCfield, just curious, you multiply the battery pack mA rating x 1.4 (where does the 1.4 come from or is it some kind of a factor)? Just trying to understand all of this battery charging stuff.

The only way to truly determine you're personal cutoff voltage for flying, especially given you're apparent concern over the condition of the batteries, is to develope a discharge curve for your battery. Its easy, but time consuming. Here's how.
If you have one of the DVMs made for hobby use, just use that meter.

If you don't have a loaded DVM, you can go to Radio Shack and buy two 1W 10 Ohm power resisters. Hook one end of the resistors together by twisting them together. This will put an approximate 240 mAh load on your battery. Hook it up across the battery terminals so you can check the voltage with a volt meter. Preferrably a digital volt meter. Set it up where the resistors get plenty of air, and don't have it sitting on anything flammable. The resistors will get hot.

Now hook up your rig (DVM or resistors) and start plotting the battery voltage against time. Check the voltage every two minutes. Be precise.

Your voltage curve should look something like the graph below.
Brad

thanks for posting the voltage curve! that is a really good idea.

I am expecting new NiMH batteries this week, should I expect the voltage curve to change over time or remain constant for many seasons of use? I guess as they age eventually the cut off will become sooner and sharper?

reason is charging batteries is not 100% efficient but I don't use 1.4 myself. I charge a couple of hours over what math says (or longer)or use a peak detect charger.

If you look on Tower's website, there is a list of things that the item "includes", such as batteries. They list 600mah batteries for both Tx and Rx. But, since you'd be buying batteries from another vendor, you can definitely wait to get them; it will be days to weeks before you are ready to start installing batteries in anything.

I think I got the 1.4 factor from either Radical RC or from Battery University (maybe they're the same?) Either way a good reputable source. And like Missileman, I just charge a few hours over what the math says to charge; the factor of 1.4 is just a way of explaining that you need to charge longer than what the math says.