OK:
New to sport. I have a trainer {Futaba radios} that I replaced the receiver battery with a 4.8V/1650 mah NIMH battery. My wall charger is only a 50 mah charger.
1. I've been told this wall charger will not fully charge to 1650 mah. true?
2. If so, I need to buy a charger that will {assuming the 1/10 rule} charge at 165 mah for 10 hours to completely charge. true?
3. I've been told the ACE Digipulse charger is a good one. true?
4. Beginner question: Why not just buy a quick field charger and do it this way all the time? Is this not good for the battery?

No, it's not true. It will charge it, but it will take quite a while.
Sounds about right.
Don't know, haven't studied that model. I've got a Hobbico Accucycle Elite. I use it for 4.8 and 6.0 volt receiver packs, lipos, transmitter batteries, and other stuff. Works great. The things I like are it automatically figures out the current based on the battery selected, it can charge/discharge 2 batteries at one time, and it comes with a 110 volt power supply, but can also work off a 12 volt battery.
Quick charging puts more stress on batteries. If you have the time, it's better to slow charge them. For additional reading, I suggest going to Red's R/C Battery Clinic. He's got lots of great info. http://www.rcbatteryclinic.com/

Buy a Sirius charger and be done with it. They are the best chargers available IMO. I charge both rx and tx with mine and havn't used a wall charger in 6 years. Central Hobbies sells them for a little over $100 online.

Cheers and enjoy!

1. The problem with charging below 1/10 C is that internal cell losses become a significant % of the charge current. The result is the charger spends a lot of its energy on just keeping the cells from discharging, and little goes into actually charging the pack. While technically it may be possible to charge a battery at less than 1/10 C, it is far from ideal.

2. 165ma charge rate is 1/10 C for a 1650mah pack. This is the ideal trickle, or slow charge rate. Don’t need to exactly hit this figure, i.e. 150ma or 200ma is close enough. You could however charge much faster if you want too.

3. I’m not familiar with the ACE. I’ve heard of it, but I’ve never used one. I use Sirius and Triton chargers. Mainly I use the Sirius chargers, and just use the Tritons for LiPos and pack capacity testing. Both the Sirius and Triton are very fine and work well.

4. You can quick field charge, but it is a bit harder on the pack. It will shorten the life (number of charge/discharge cycles) of the pack. Some cells deal better with high charge rates as they are designed for this use, other cells do worse. The actual reduction in battery life is generally not terribly significant if you keep the charge rate at 1C or below, but it will depend on the cells. In general, I charge nearly everything at 0.5C to 1C. But occasionally I will trickle charge a pack to help balance cells and perform a discharge to test capacity. So in that respect, it may be a good idea also have a way to trickle charge and to test pack capacity. This could be the same unit as the charger, or separate unit(s.)

Howdy, I have been using the wall charger that came with my Airtronics radio the packs and radio are 1 yr. old my tx. now only charges to 10.5 volts when it used to hit 11.2 or more right off the charger. I am wondering what should I do and about how to cycle them Ive run them down and recharged several times in the last year I'm afraid my capacity has went out the window, don't know about the reciever pack haven't checked it with a voltmeter in a long time some advice please. Thanks

sounds like you may have a dead or dieing cell. My advice would be to first test the batteries on another charger(to make shure its not your charger), and if they still dont hold, get a new one. Its not worth a battery dieing in the middle of a flight when i think the big 2100mah pack dont cost but 40$ or so...