Battery Selection
The 9XR radios require an input voltage between 6 and 13 volts, allowing use of many different batteries. The main options are outlined below.
The 9XR battery connector is compatible only with a JST plug of the type used for the balance lead on a 3s LiPo/LiFe battery. This means that such a battery can safely be plugged directly into the 9XR. Other types of battery may require fitting a JST-XH 4 pin plug. Only the outer two wires are used: in the transmitter socket the left pin is negative (black) and the right one is positive (red). Be extremely careful about polarity. Check the polarity of any battery before plugging in.
The minimum practical battery capacity is about 800 mAh (milliampere-hour) but batteries in the 1500-2500 mAh range are normally used. These should give at least 10 hours of operation.
The Turnigy 9XR Safety Protected 11.1v (3s) 2200mAh 1.5C Transmitter Pack
This is the battery sold by HobbyKing specifically for the 9XR series of radios. It is a low cost, low discharge rate Lithium Polymer battery which includes a regulator that is claimed to allow it to be charged at a low rate while still in the transmitter. The charger used must deliver less than 0.3 Amps (300 mA) at 12 volts. If the battery is almost fully discharged and a typical 150 mA charger is used, charging may take about 24 hours. The charger jack has the centre pin positive. This is the same as Futaba chargers but opposite JR and Spektrum chargers.
Note that the 9XR radio has a 0.3Amp fuse in the charging circuit to protect the transmitter and battery. This will burn out if subjected to a higher current and is difficult to change.
The battery may be charged outside the transmitter at much higher rates using a proper balancing LiPo charger. The recommended charge rate is 0.5 C, i.e., 1.1 Amps, at which rate a full charge will take about 2 hours. The maximum charge rate is 2.2 Amps.
Even though the battery (unlike other LiPos) can be charged in the transmitter through the charge jack, balance charging out of the transmitter with a proper LiPo charger is strongly recommended.
Because the battery has a low voltage protection circuit that shuts off power to the transmitter at between 9.6 and 10.0 volts, it is very important that the transmitter voltage alarm be set well above that level: a setting of at least 3.6 volts per cell (i.e., 10.8 volts for 3s) is recommended.
“Any Old 3s LiPo”
Any 3S 11.1 volt LiPo battery that will fit into the battery compartment can be used to power the transmitter. Such batteries must be charged out of the transmitter with a proper balancing LiPo charger. At the recommended charge rate of 1C, charging will take about an hour. Note that charging a regular LiPo with a NiMH or NiCd charger will destroy the battery and could start a fire.
To avoid the risk of battery damage or even fire and to ensure that enough energy remains to allow a safe landing, it is recommended that the low voltage alarm be set to at least 3.6 volts per cell (10.8 volts for 3s)
LiFe (Lithium-Iron)
A very inexpensive 3s 1500 mAh LiFe battery specifically for transmitters is available. LiFe batteries are safer than LiPo but still need proper handling. For example, if allowed to discharge fully (by leaving the transmitter turned on) they will be damaged and not be rechargeable in the normal way. Instructions for recovery can be found online but seldom work more than once with a given battery. The typical maximum charge voltage is 10.8 volts, but the battery settles back to 9.9 volts within the first few minutes of use and declines very slowly over the discharge.Of the three leads on the battery, only the balance lead will fit the 9XR.It is recommended to set the low voltage alarm at 9.3 volts. At the recommended rate of 1.5A, charging will take about an hour.
The battery must be charged out of the transmitter with a charger specifically designed for LiFe/A123 type batteries. Charging with a NiMH or NiCd charger will probably destroy the battery.
NiMH
AA-size NiMh cells can be made up into a reliable, safe pack suitable for air travel. Low self- discharge (LSD) should be used. For the 9XR, a six-cell pack is the largest that will fit in the battery compartment.You will need to fit a JST-XH 4 pin balance lead connector (only the outer wires are used). The battery will show about 8.5v immediately after charging and can be discharged to a safe minimum of about 6.6v. Hence such a pack is well within the 9XR voltage limits. The battery may be charged whilst installed in the radio but the charger used must deliver less than 0.3 Amps (300 mA) at 12 volts. If the battery is almost fully discharged and a typical 150 mA charger is used, charging may take up to 24 hours. Higher charging rates may be used with the battery removed from the radio using an intelligent peak-detect charger on the NiMh setting. Refer to the charger manufacturers instructions for the correct method.
It is recommended to set the low voltage alarm to about 7.0 Volts for a 6 cell pack, thus allowing ample headroom for the transmitter regulators and giving the pilot plenty of time to land.
Li-Ion
Packs of two Li-Ion cells may be used in the 9XR transmitter. Cells are available with built in regulators. Capacity varies from 800 to 3200 mAh for the same physical dimensions (the capacity is usually overstated). Typical specifications for anUltrafire 18650 3200 mAh Rechargeable Battery: Length 67 mm, Diameter 11 mm.
The regulator limits the charge current to 1.5 Amps, so charging time will be around two hours for a near-empty 3200 mAh pack. Care must be taken when soldering leads to the ends of the battery not to apply too much heat so as not to damage the regulator. You will need to fit a JST-XH 4 pin balance lead connector (be super careful to get the polarity right!). These cells require the use of a charger capable of charging Li-Ion cells.
These cells charge to 8.4 volts but quickly assume a consistent delivery at about 7.4 to 7.6 Volts for most of the discharge. The minimum voltage to avoid battery damage is 6.5 Volts, but it is recommended to set the low voltage alarm at 7.0 volts to allowample headroom for the transmitter regulators (and time to land!).