Someone at my club suggested I switch from nickel metal hydride to lithium ion (not lithium poly) batteries for longer life. I have a Futaba 7C 2.4GHz radio and R617FS 7 channel receiver. Two questions:

Can someone recommend a good brand and voltage/amperage rating to go with for long life and fewer required charges?

Can I use a 7.4 or 6 volt instead of 4.8 volt, in addition to a high amperage like 2400mah without making any other changes?

I thought about doing the same thing, but most people on here told me it wasn't worth it. You can do 6 volt no problem, you could even put 5 2400mah energizer AA's together if you knew what you were doing. I did it with my rc truck, but don't trust my soldering to the risk of it being in an airplane. There are high capacity nicd & nimh tx packs out there for much less than a lipo.

Yeah, I have hi capacity nickel metal hydride packs already and they last alot longer than the lower amperage nicads I had, but this guy made it sound like he could fly for a month or more without a charge with lithium ions. The only ones I found were 7.4 packs on all-battery.com and they're
like $37 for a 4400 mah pack which is plenty for me. I'd gladly spend that if I didn't have to charge for that long.I would continue to check my batteries before each flight but it'd be nice not to have to charge them for such a long time. I just want to make sure I can use them and if so do I need a regulator or anything.

That was one thing I remember someone mentioning was a regulator. A tx pack fully charged would be at 12.6V, not sure if that would damage a tx without a regulator or not. The lipos may hold a charge better when not in use, that may be how he gets away with hardly ever charging.

Are you having a problem with your current batteries? If not then there's no real need to switch.

The guy saying he can fly for a month without recharging would be foolish to not fully charge his batteries before a day of flying no matter what battery chemistry he is using.

Each battery type does bring some sort of advantage to the table as well as some sort of disadvantage. For the typical sport type planes that the vast majority of us fly NiCads and NimH are low cost, easy to work with and provide great reliability.

The only other batteries out there that really interest me are A-123's. I may give them a shot on the next larger plane I put together.

No,I'm not having a problem with my current batteries.I would be willing to spend the amount I mentioned if I could go without charging for multiple days, even weeks.

Why charge a battery when it doesn't need it just because it's a new day of flying? The guy I mentioned is definetely not a fool. He's one of the most careful fliers at our field. He checks his batteries before every flight. And does a radio check from distances you wouldn't believe. He does tend to go for the top of the line in everything he does. Of course he has larger planes too. To each his own. If he suggested the lithium ions, I respect his opinion.

Chuck, don't you have to regulate them. 7.2 nominal may be to much for the servos and receiver. I don't know what the fully charged voltage will be. I've been looking at them also. I've got a 33% that has batteries in it, but I'm not sure what they are, I just got the plane and haven't stripped it yet. I know that there is at least three packs in it. 'll probably put in a distribution setup with a regulator, of some kind.

The other plane I got from the same guy is a 1/4 scale with some monster 4.8V 1200mah packs from Airtronics. They look like sub C cells. They will go and I'll replace them with some 6VNiMh 2300mah packs or similuar. I want the extra torque from the 6V packs. The four main servos are JR 8101's in this guy.

Don.

I used to own a GMC pickup with dual tanks. Man that was great, you always had a reserve. If you run out on one tank, hit the switch and you were good to go. That was the theory, but in practice, I ran out of gas in that truck more times than all my other cars and truck I've ever owned combined. It's just to easy to "fall back on the reserv" and not keep the tank full. Same goes with batteries.

I've got some 2300mah NiMh 4.8V packs in a couple of my planes. They hold a charge for quite a while. To the point that when I go to the field, I check the voltage and it it isn't full, I field charge it at the field. Unless it's been aweek or so since I last flew theplane, I don't chargethem at home now. However, the plane is fully charged for the first flight each day.

Don

Didn't mean to come off that way. I do disagree on the charging though. Even if the useable battery capacity was so high and the self discharge rate so low that you could fly for days without recharging, why chance it? Why not start each day at 100%? I view RC planes as not much different than full scale planes. Any risk that can be minimized or prevented before flying should be. Charging takes almost no effort so I figure why not do it? That's just my approach to the hobby. I've seen a lot of planes crashed and the pilot then saying "I thought it was good enough".

I'm not sure on the A-123's. I haven't gotten too far in my research yet. Ithink a 2-cell has a nominal voltage of 6.6V but Imight be wrong. It's a "one of these day's I'm gonna learn more and try it" type of thing.

I respectfully disagree. I'm not talking about chancing a flight when my batteries are marginal. By your logic, why wouldn't you have to charge the batteries before every flight? Plus, can't you shorten a battery's life by overcharging it, repeatedly, over and over again, when it doesn't need charging?

I'm not talking about charges between flights (although checking between flights is a good idea). Just between flying days. The plane is sitting there doing nothing the night before going to the field so why not charge it? Shortening the life through charging really depends on the battery chemistry, the charge rate, type of charger, etc. I believe. That's the good thing about charging before a day of flying, you have time to charge at a lower rate which is much better for the battery in the long run. Regardless, I'd rather use a up a few battery cycles if that were the case than lose a plane. That's just how I see it. I'm one of those very thorough, meticulous types that likes to take care of every little detail, leaving as little as possible to chance.

If you want to put a LiPo pack in your TX, and you're worried about the 12.6V being too high, you can just put a diode in series with the positive lead (forward biassed, of course) to drop the voltage. I've heard of several guys putting them in w/o the diodes and not having a problem, but I remember seeing an advisory from one of the major manufacturers warning that they've seen radios returned with damage due to the higher voltage of the LiPo pack.

The other reason to put a diode in series with the positive lead of the pack is to block the external charge jack from the battery. If you forget you have a LiPo in there, and plug in the standard radio wall wart, you'll probably destroy your LiPo pack and radio! The diode will keep you from charging through the power lead, so you'll be forced to use the balancing connectors for charging.

I'm considering getting one or two of these TX packs from HobbyCity, and I'd put a diode in series to drop the voltage, just to be safe:

Rhino TX LiPo Pack

Zippy TX LiPo Pack

The cool thing about these packs, is they have a Futaba connector, JR/Spektrum connector, and a balancing connector, so you could use the same pack in just about any brand of radio. Unfortunately it looks like they are out of stock right now.

You know,... yesterday I visited a hobby shop and probed about lipo's in my plane with a regulator, after reading all the specs on all of them, you can't use a 3 cell on any of them, only 2 cell, I shy'd away, due to the fact that I only own 3 cell 2200-3000 MAH lipos. So even that fancy spectrum fan cooled 10 amp regulator, which wasn't the most exspensive, couldn't handle 3 cell lipos, and didn't seem to give me confidence in the fact that it shuts down if voltage hits 6 volts.

It's not clear from the original post if he is asking about TX or RX batteries.

I'm using the packs PKH listed on JR, Hitec and Polk transmitters without any problems what-so-ever.
I do charge the LiPo's via an external charger though.

For receiver batteries, I also use LiPos as they are lighter than equivalent NiMH or NiCD's.

However I always use a BEC on my planes when I'm powering the electronics with LiPo's.

JR sells BEC and regulators, but I've been using Turnigy 8A output regulators on my medium planes and up.

On smaller planes I use the same smaller 5A BECs often used in electrics.