I have been flying my Raptors with an A123 2300 RX pack and all is good, I love the Hitec system. My question is about a new 90 size H9 P51. I have a 1650ma NiMH 4 cell pack installed. I have low current servos (non digital) in the plane but I do have 2 JR 4721 servos. Will I have any problems using a 4 cell pack? I have an A123 pack for the plane but the JR 4721's do not work well at the higher voltage.

JR Servos - Warranty void most JR servos used above 4.8V - Do not use above 6.0v fixed. is correct.

Whilst a 1650 NiMH pack would not normally be a problem, dueto the verydifferingresistances, it certainly will cause problemsif the cells are smaller than AA size such as the AEor AAA used in some lightweight RCapplications. NB: Never fast charge AANiMHreceiver packs.
Aurora A9 - Battery is not charged.has some good information on NiMH batteries.
A123 cells, use with caution, pleasecheck specs against Optima Transceiver (RX) - A123 2S Cell
<span style="font-size: smaller">- Low Battery Warning </span><font size="1">not adjustable V1.04&lt;06. How to set alert voltages V1.07. Warning regarding use of Eneloop &amp; A123 2S as RX batteries.

<span style="font-size: x-small">The Optima receivers provide a Supplementary Power Connection. This is a dedicated receiver power supply which is not affected by any fluctuations on the servo side and"brownouts", unless uncharged/faulty battery is used,are negated. Simply install another switch and a small 2S lipo or another small RXbattery as detailed Optima Transceiver (RX) - SPC

H9 P51 can easily carry an extra RX battery:
Optima Transceiver (RX) - Multiple Batteries may be installed.
Dual batteries for redundancy or even one for each servo, mayprovide furtherpeace of mind.
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</span></font><span style="font-size: smaller">more:
Aurora A9, Spectra Pro &amp; Optima - FAQ &amp; Undocumented Features - Mixes, Setups, Tips. {Individual Links often updated}</span><font size="1"><span style="font-size: x-small">

Regards
Alan T.
Alan's Hobby, Model &amp; RC FAQ Web Links
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Thanks for the info. I am using true A123 cells from Andy Low (ElectroDynamics) and I use his checker. I know how much is used for each flight (average) and I know when to stop flying. I did not know about JR servos not being rated for 6 volts. The specs show a torque and speed at 6 volts.

Hey, tell me a little about that hot looking airplane in your avatar!
Thanks

That is a Super Reaper, It has a Ram 750 turbine on it. I have been flying it for a few years now. I have not converted it over to 2.4 yet but plan to in the future.